Because I practice them a lot and the dynamics of a real x-wind landing is not reproducible in a home sim. You can practice where to put the controls. But in a trainer like a 172 or DA20 you can’t practice the forces you feel pushing back at you and the other seat-of-pants aspects.

One of the drills I do is to descend to 50ft over the runway and then hold the plane on centerline in a eg 20kt crosswind. The sim just can’t even come close to how dynamic and effective that exercise is. Also the feeling of putting down one wheel first, feeling the bump, then the other. The slight skid and side g forces of you mess it up slightly. Those kinds of things.

There are many things that sims can’t reproduce that don’t matter that much when it comes to productive learning. But with cross wind landings, these things matter a lot.

I’m specifically referring to home simulators and MSFS and X-plane specifically. I have no experience in full motion commercial jet or military sims.