Is there any reason why mostly technology deprived planets are pictured in the Star Wars movies?

Frankly, Lucas wanted giant mega cities and shiny tech everywhere. But Money and Technology just wasn't there at the time. According to wikipedia:

The concept of a city planet in the Star Wars universe originated with the initial drafts of Star Wars Episode IV: A New Hope. The planet was called Alderaan, and much of the action in the film transpired on it. Since building such a city would be prohibitively expensive, much of what was to take place on the planet was moved to the Death Star, and Alderaan became the name of Princess Leia's home planet.

The Empire's homeworld, Had Abaddon, came up in early drafts of Return of the Jedi. The entire planet was to be a sprawling city. However, concluding that the realization of such a city was (still) impossible at the time, the creators abandoned the idea.

The idea of city planets, i.e. a planet so urbanized and technologically changed that the entire planet is a single city, was eventually shown as Coruscant, the Republic mega-city-planet in the 1997 special edition of Return of the Jedi, and eventually the Prequel Trilogy.

Lucas himself confirmed it in an interview about Illustrated Light & Magic special effects studio:

“It was like a giant switch was thrown overnight,” Ed Catmull says about Jurassic Park’s effect on Hollywood. CG began to spread everywhere, with movies being green-lit on the strength of a single test shot. Projects once thought impossible became possible—and for Lucas, that meant his long-imagined but never-realized Star Wars prequels.

LUCAS: I never thought I’d do the Star Wars prequels, because there was no real way I could get Yoda to fight. There was no way I could go over Coruscant, this giant city-planet. But once you had digital, there was no end to what you could do.

And that's why we got the Prequels and their cg eyesores wonders of digital technology.

To add onto the other useful answers here, Star Wars is usually considered a Space Western.

A characteristic of the genre is that you usually don't see major urban centers, as westerns usually take place on the edges of civilization, where the law is weak and adventure can be imagined.

Low-tech is relative.

Sure, Tatooine is a desert hell-hole with moisture vaporators and everything. But they have plenty of technology - just not as much as other places, which is also very much related to the fact that Tatooine is very sparsely populated.

The typical example of a very high-tech world would be something like Coruscant - a planet-wide city with a huge density of population and lots of opportunities to flaunt your riches (imagined or otherwise).

What's the main difference between the two? Capital.

Technology doesn't come out of nothing, it comes out of investment - someone delays their own consumption in order to do an investment that will mean more (capacity for) consumption in the future. And as our own planet shows, opportunities for investment even on a single planet seem to be rather unlimited, just like human needs are unlimited. Whenever there was a "jump" in technological level on Earth, it meant that people accomodated to the new standard, and wanted more again. If this were not the case, Earth would already be a unified (relatively) high-tech world - that is, no areas would have lower level of technology and capital than others.

Investing capital means trying to find the best return on your investment in a certain amount of time. That's why high-tech countries remain high-tech, while low-tech countries remain low-tech - again, relatively. When you add more capital to a low-tech country, you "advance" it, but you're going to be investing in things that have the best return on your investment. So you're not going to build a car design shop in the middle of a desert occupied by a native tribe that doesn't understand one bit about physics (which would require a huge investment that could be avoided by building the shop in your country), but you might want to build up a mining operation there, and get maximum from lower wages and better worker motivation. As a side-effect, you make everyone's life better - but your only concern is return on investment. The same kind of mine in your home country would be much more expensive.

Now, let's see how this works for Star Wars. Obviously, they didn't reach the limits yet - there's still opportunities to invest capital, both at home and abroad. Somebody colonized Tatooine at some point, expecting some return on the investment (even if that was something like "avoiding racial discrimination" or whatever). But Tatooine is full of people that are simple moisture farmers (who might own huge swathes of land!), with very little education and very little added value compared to people on other worlds, low-tech or not. They still have access to high-tech gadgets (because they're still part of the same economy), but they're expensive compared to their own income, so they're not abundant.

Coruscant is the kind of world that's a target of investment even ignoring all natural resources and local population etc., simply because it's an important hub system, not to mention the seat of the government. You want to have some presence. But worlds like Naboo and Alderaan are very similar - high-tech societies with very limited primary economies and lots of capital. They also seem to be rather hospitable, presumably with plenty of natural resources, at least in the past.

A big deal is made out of the contrast between the Core Worlds and the Outer Rim - this means that it's quite probably that the Core Worlds were on average settled earlier. There are some cases of Rim worlds that are actually high-tech, so time is not the only concern - most likely, the worlds in question had some important advantages for capital investment compared to the Core Worlds - for example, cheap land with plenty of resources, or even just low or non-existent taxation for example.

Throughout history, one thing has almost always been true - where economy blossoms, states get interested and invested very quickly. They want their "fair share" of the bounty. So the more high-tech the world, the more capital it has, the more presence the government would have as well. And now we come to the crux: episodes IV-VII follow people who are actively avoiding the authorities. All thing equal, they'll try to keep as far away from the high-tech worlds as possible.

The Rebel Alliance specifically targets planets that are underdeveloped for occupation - in fact, ideally entirely abandoned or unknown. Obviously, they also have bases on planets like Corruscant, to handle espionage and recruiting (in support or personnel), but that's not where you park your war fleet. Luke lived his whole life on a backwater planet, which echoes the typical "unhappy with a farmer's life" story, but it also reflects other things: maybe the imperial propaganda isn't so strong on backwater worlds (not enough population to bother), and the imperial presence makes it easier to move untracked. A poor guy has less to lose than a rich guy with his own business, as long as the rich guy isn't specifically fighting against losing his business. The core of the Rebel Alliance were the elite guys of the old Republic, but it's quite possible that the brunt of the Alliance were backwater guys looking for freedom and adventure.

Some great long considered answers here. My simple theory which enables me to get lost in the movie is, if you can have cell phones and networks in "Low Tech" African nations you can have Light Sabres, Droids and energy shield on Tatooine.

well, ask yourself this...with all the technology in our world alone, why are there still countries with no, or even bare minimum technology? Same kind of reason. In deserts around our world, you don't see a whole lot of tech either. In poor countries you don't see a lot of tech. In Star Wars, this is no different.