because realistic graphics are much more appealing to look at

In your opinion.  Other people like Cel Shaded graphics.  Still other people like 2D graphics.

And still other people are fine with any kind of design choice.

Also, there's plenty of 3D games that don't have 'realistic' graphics or cel shaded graphics.

I can understand games like The Wind Waker and Eternal Sonata to have cel-shaded graphics, but i can't imagine games like Fight Night and Gears of War to have cel-shaded graphics. With that said, in my opinion, cel-shaded graphics are not be best choice for mature games.

A cel-shaded Gears of War would be super cool if it turned out as I picture it inside my head. Characters already look a bit deformed and using a more darker style of cel-shading (no manga style!!!) it could turn out well.

Look into my head and you'll know what I'm talking about.

I think it really boils down to animation still being largely considered for kids (and by that I mean really young ones) in the west. The ones that are not seem to be usually just comedy/satire driven.

Mind you, anime is not the grown up thing a lot of people seem to believe it to be in Japan, but there is still a lot of it targeting teenage audience, across various genres.