The environment that SXS's are subjected to is also a big factor. The fine dust that gets pulled through a SXS's CVT is grit that wears on all of the components. I've never had to do major CVT surgery to any of the sleds I've owned (other than adjusting springs and weights) I had to replace the entire clutch in my RZR XP 1000. (the previous owner knew nothing about CVT's)
@Biffdotorg is correct, stock clutches are designed so that the sheaves slap together to engage and not come together slowly and slip. (a buddy of mine is a retired Polaris engineer and reminds me of it if he sees me easing into it)