It was economics like with most hardware of the time. Those were expensive, custom machines. The CISC and RIZC processors kept getting cheaper and faster to point that users, mostly wanting performance, were better off buying them. Genera itself eventually got hosted as an emulator or something on Alphas. Then Alphas bit the dust haha. Wait, it's not funny cuz PALcode was amazing.

Anyway, economics and market demand as usual. That's what killed it.