A lot of people don't really need to go Full k8s, but I think swarm died in part because for many users there was -some- part of k8s that swarm didn't have, and the 'some' varied wildly between users so k8s was something they could converge on.

(note "died in part" because there's the obvious hype cycle and resume driven development aspects but I think arguably those kicked in -after- the above effect)