Do you solely GM? When you play, do your instincts about what makes up a reasonably balanced yet challenging game vanish? Aren't many players also GMs and vice versa? Is it a quality of the role in the game that causes the phenomenon, or is it a quality of the person?
I GM quite a lot, but I also play. I don't tend to look at the games I play in as somehow less "mine". I'm responsible for how those games go. I'm not solely responsible. But I'm not solely responsible for how the games I GM go, either.
Perhaps it's the sharing of responsibility for the game that makes players less likely to scramble for every competitive advantage? Perhaps withholding the ability to have input on the game makes folks desperate for any bit they're allowed?
I don't know.... there seem to be some odd correlations here.