I'd say that's quite simple, people have an expectation of what a game should cost - and a large majority of them wouldn't take a second glance at a product that places itself wildly outside the expected range. Lets take movies as a comparison, their production cost varies immensely too, but a cinema ticket - although the prices have risen over time, costs the same regardless of which film you go to see. The only variable is how many people go to see the movie. I can't claim perfect memory, but best I recall the same goes for dvd's, too. By which i mean, cinema-movies being released on dvd, not straight-to-tape releases which obviously tend to be priced lower.
And that's why they spend seemingly impossible amounts on marketing, and why high production value media often seems "generic", because reaching the largest possible audience is their only means of getting a return on investment.
Also, since most games nowadays are released digitally, people can't re-sell them - which I'd bet adds to their hesitance to pay a high price up-front. That's a whole separate discussion, really, by all logical standards digital and physical releases should be priced very differently, but as far as I'm aware they aren't at all.
At the end of the day it's all just a symptom of the (current(?)) economic system; everything needs to be bigger than last year's, because that's the only way to keep investors happy. Their goal isn't to sell videogames or movies, but to grow. Amazon is the perfect example; Why don't they pay any taxes? Because they have no net profit, everything is reinvested immediately, because growth is the only goal.