Stop bieing a faggot bitching about casualgate because this has been an issue long before comicsgate was even a thing. What you described isn't even what happens, ffs.
Marvel overships and runs variant scams. With overshipping, if a store orders 20 and Marvel sends 50, those 30 extra books are "free". But the shop has to pay Diamond's shipping/handling fee, and now has to figure out what to do with the extra books they didn't want. The extra books count as units shipped for Marvel's Diamond figures, but not dollars, and the store has to waste shelf and floor space for them. If the shop doesn't pay for the extra shipping, the whole order gets denied.
With variants, normally if a shop wants X copies of whatever incentive variant, they have to buy X amount of that issue's regular cover (1:10, 1:25, etc). What Marvel sometimes does is say that the shop has to buy X amount of some other book's issues instead, to give that other book an artificial sales boost. Their recent lenticular variants debacle was notably bad about that.