It’s not the IS that makes them expensive, it’s the locked out ecosystem and the monopoly they have. I’m not saying they’re not good - they are (from what I’ve seen), but healthy competition, if it existed, would’ve driven the prices down a bit.

As for IS itself, since the move to IBIS, it makes sense that some lenses drop the IS and only rely on the body’s. IMO it used to matter in the DSLR days when IBIS was not really a thing. Nowadays it’s sensible to only put it into the longer lenses that physically need it (the longer the lens, the more physical movement required to compensate and so on).