Why was "The Social Network" made so quickly after Facebook took off?

In some ways, asking "what's the reason for this" might be a non-starter of a question, because the ultimate reason for why any movie is made is that a producer thinks it's a good idea. And certainly, the fact that Facebook was made open to everyone late in 2006 makes it seem like the time frame is pretty compressed to get the movie out, but it's important to remember that Facebook had been around for several years before that -- every college kid in the US knew about it by late 2004. So even if Sorkin started his research in 2008, that's 4 years after it became clear that this could be a good story, far less time than it took for Zero Dark Thirty to be released and pretty comparable to United 93.

I think it's also important to note that Sorkin (and Sony Pictures who produced it) didn't come up with the idea; rather, the publisher of the book The Accidental Billionaires was actively selling the film rights before the book ever came out. According to an interview that Sorkin gave:

You still have to find Waldo in there somewhere. Here’s how it started: I got a 14-page book proposal that Ben Mezrich had written for his publisher for a book he was going to call The Accidental Billionaires. The publisher was simultaneously shopping it around for a film sale. That’s how it wound up in my hands. I was reading it and somewhere on page three I said yes. It was the fastest I said yes to anything.

But Ben hadn’t written the book yet, and I assumed that Sony was going to want me to wait for Ben to write the book, and I would start a year from now. They wanted me to start right away. Ben and I were kind of doing our research at the same time, sort of along parallel lines.

( from http://www.wga.org/content/default.aspx?id=4348)

As we already know that 'The Social Network' was based on a book called 'The Accidental Billionaires' by Ben Mezrich. Now if you check the wikipedia entry it tells us something about the production.

Screenwriter Aaron Sorkin said, "What attracted me to [the film project] had nothing to do with Facebook. The invention itself is as modern as it gets, but the story is as old as storytelling; the themes of friendship, loyalty, jealousy, class and power. I got a 14-page book proposal that Ben Mezrich had written for his publisher for a book he was going to call The Accidental Billionaires. The publisher was simultaneously shopping it around for a film sale. That's how it wound up in my hands. I was reading it and somewhere on page three I said yes. It was the fastest I said yes to anything. But Ben hadn't written the book yet, and I assumed that Sony was going to want me to wait for Ben to write the book, and I would start a year from now. They wanted me to start right away. Ben and I were kind of doing our research at the same time, sort of along parallel lines."

However, according to Sorkin, Mezrich did not send him material from his book as he wrote it: "Two or three times we'd get together. I'd go to Boston, or we'd meet in New York and kind of compare notes and share information, but I didn't see the book until he was done with it. By the time I saw the book, I was probably 80 percent done with the screenplay." Sorkin elaborated:

So it's like the book and the screenplay for this movie were almost written in parallel.

So when the book was released in 2009, pretty soon the movie als got released in 2010. So my point is - The Social Network's production just followed the production of the book - The Accidental Billionaires. And the book followed what was an interesting story at that time. So it is only coincidental that the movie's release and facebook's boom occured at the same time.