What, exactly, are people doing that causes their jeans to wear at the crotch? I’ve never had shorts, jeans or any other trouser-type item wear through there; through the ass, yes, ‘cos that’s what I sit on and which gets most wear.
Sounds like you sit on your ass a lot whilst other of us walk about a lot (and hence wear the crotch).
In all seriousness I imagine there are various factors including the material, your body shape, walking style, fit of trousers etc. Some denim / material is definitely more robust. I only tend to get the wear in trousers I wear a lot be it my jeans (such as my dog walking ones) or my work trousers.
Thinking of my dog walking jeans I currently use a pair of Wranglers which I picked up cheap at TK Maxx and they have worn incredibly well.