because those are the cheap chinese ones fox sells. Everyone buys them because fox has a good name in the off road industry on their high dollar shocks, so they assume the cheap ones are good. Not, you get what you pay for there.
unless you are buying a fox shock like this
https://www.ridefox.com/subhome.php?m=offroad
or something that is a bolt in factory shock that looks similar, its going to be junk.
a rancho shock is better at longevity as well as bilstein 5150's.
The fox shocks that come on rzr's and canam's are even cheaper crap than the offroad factory race series you can buy. the rzr's/canams have plastic IFP's inside, stupid needle caps for nitrogen, and aluminum bodies that gall up the moment you try to adjust shock preload. they dont tend to hold up well in a race environment either