I've asked the same question myself. :-)
I think its the same reason why low rated players usually dont resign even when they havent got a single thing on the board (except the king) and just wait till they get checkmated. At lower level they probably make mistakes and blunder things, so one side usually has an advantage. In Soccer, you'll see and U10's match or something and almost always the game has more the 5 goals in it. But when it comes to the proffessionals they hardly ever make mistakes, thats why only 1 or 2 goals only happen in a soccer match.
At GM level in chess the game is often drawn, as both sides just dont make any mistakes, so few that there is no breakthrough and a draw is agreed. Thats what I think anyways.
I notice a lot of times at lower levels of play I won't see draws except an occasional stale mate.
At mid level of play I see some draws, maybe one out of 5 or one out of 10 games.
However at the GM level of play I see almost half the games being a draw.
So is it the more often you draw the higher your rating?