Because we're in the adolescence stage in the growth of a medium.
I remember when I was about 13, I used to skateboard. I LOVED skateboarding to a pretty obsessive level. I wrote the brands of the decks on my bookbag in white-out, got excited looking over CCS catalogues, researched what wheels are better and why, which trucks are more durable, what shoes would be better, and even though I couldn't so much as kickflip, developed a connoisseur complex about it. I listened to nothing but what I thought was punk rock and shunned rap music along with anything other than fast power-chord rock that I could skate to.
To relate that to games...
The flexibility the medium has attained in expressing itself artistically is nothing short of staggering. We've never been more able to create art of all kinds within the medium of games as we are now. So naturally, we obsess over the idea. We champion the names of indie devs in forums, toss around the word "beautiful" whenever a game shows an iota of something other than photorealism in its graphics, research what gameplay and storytelling techniques work and why, then we create sites like The Escapist to post our thoughts and essays and articles about them in...and naturally, we develop a superiority complex. We begin to wish the AAA releases weren't so samey-looking. We develop a disdain for big corporations and sequels and remakes, while we champion and overrate indie developers for being "fresh" and "original." And eventually we disdain the people who begin to disagree.
Until we grow up.
It's just adolescence. Once the idea of artsy games isn't so new anymore, or once we collectively grow up as a community, there'll be a lot less (vocal) pretentiousness and arrogance. Whichever comes first, though.