Power
While you won't get paid, you may be able to wield a modicum of power over film studios if your blog—er, sorry, professional critique—develops a big following.
You know the whole "pen is mightier than the sword" thing? It can be for real, especially in the movie business.
For studios that spend millions on a film's production and release, a sharp, snarky review by a popular film critic that compares their film to watching paint dry (if, somehow, paint drying was less exciting) can be the death knell that keeps their key demographic away.
The movie industry is suffering enough trying to convince people to shell out what amounts to the price of a two-month Netflix subscription for a ticket. People are expecting instant gratification or else—and they look to the film critic to tell them whether it's worth it.
Of course, you could always eschew the film critic idea and just go straight to writing propaganda for the studios and get a gig in distribution as a publicist. You'd lose the power play, but you've got to keep the lights on somehow.