The majority of people who go into a BETA don't do it to help the game, they go in to test/play the game. Not to mention the pretty large group of players who'll look for glitches they can abuse when the game is released to gain an advantage. There's also the people who play just to get reviews or let people see how the game looks.

A very small percentage of people who play in any form of BETA actually bother reporting anything they find unless it hinders the fun they're having in said BETA.