Why do film studios buy domains of fictitious companies?

My guess: people like me often visit domains in movies/TV shows/books just for fun.

If I see the domain is unregistered, I can register it myself and draw traffic from nerds like myself. Basically, I'm letting Sony advertise for me.

I can even imply movie affiliation and do terrible things:

"Welcome to Sony's secret site! You have cleverly spotted the Easter Egg and are entitled to a reward! Just enter your credit card number..."

I'm still pondering registering spear-a-boar.com a domain mentioned by Dave Barry in one of his columns.

Just a theory, but being able to buy a domain this way is a pretty clear indication that a legitimate company cannot come after the film company to sue for being libelled or defamed for a less than perfect company portrayal. If currently unused, it is an indication there is not a naming conflict to a company that is not well known.

The fact that you noticed this from The Blacklist, which deals in companies on the shady side, including terrorism, corporate espionage, and similar, makes this a very likely financial decision on the part of the production company.

Two reasons:

1. So that the film company doesn't lose out on a potential profit if someone buys a domain name associated with a movie/TV show and sells it. Apparently there's a small culture out there to purchase domain names related to a recently-announced movie/TV show, as when the movie company finds out its already registered most of the time they'll pay hundreds if not thousands to snag the domain name off you.
2. So that the domain name isn't used maliciously by a third-party. Movie companies also buy-out phone numbers used by their movies; this too happens in other industries such as gaming. A notable example of this is when players of Grand Theft Auto 3 found that a phone number within the game led to a phone-sex line if called (this wasn't intentional).

TL;DR: It's just brand protection.

Theory 1: Trade mark ownership for future profits. Maybe they are owners of the trade mark and wish to have the option to use it for something in the future? Trade marks need to be established, one way is to use them in the marketplace so maybe buying it and owning it is marketplace activity?

I am not a lawyer, but look at this case to see that trade mark rights can be lost: http://www.novagraaf.com/en/news?newspath=/NewsItems/en/pinterest-loses-right-to-use-trademark-in-europe

Losing a licensing deal is a large sum of money lost. Hence they wish to establish ownership asap.

Theory 2: Maybe it would be a phishing site worry and they fear the bad publicity?

Theory 3: Testing for future movie promotion tricks. They are playing with the idea of very elaborate promotion websites and want to see what kind of response they get to them so far.