Why is Buzz in the videogame a toy? he should have look like a human and his armor should have looked more realistic.
Because it would have been weird.
It would also have ruined the whole “actually a video game” twist when buzz dies.
And not all video game characters are realistic, Buzz is based off a cartoon after all. If a disney animated movie becomes a video game, would they make the characters look like real people? No, they’d look like 3-D versions of their 2-D selves. Not the best example, but I can’t think of anything else.
Yeah, it’d probably get confusing with making the 2D human Buzz into a 3D model. Let’s just say it’s a video game based off the toyline. Buzz’s real appearance is in all the merchandise that Andy has in his room. The Buzz Lightyear of Star Command model’s is similar, except the real Buzz was originally supposed to have wings that fold out, like in the movie, as opposed to launching out horizontally.
Shouldn’t the title be why isn’t Buzz a human?
I agree with Dinoco
I’ve always thought the same thing. Clearly they used the “toy” model so that everyone would think it was somehow “real” before it was revealed to be a video game.
Or maybe the fictional Buss Lightyear character had been turned into a giant robot or something at that point in time (or for the purposes of the video game) which is why the video game character so closely resembles action figure Buzz.
I was going to say something, but everyone in this thread has covered all the reasons. 
You guys are way too perceptive. 
I have wondered this before. I think it would’ve been cool if they kept the same Buzz but removed the obvious toy-like features such as the screws. Most people wouldn’t notice that way, but it’d still be a subtle touch.