I think it's more that Mesos committed suicide by DCOS - which sapped the strength from the community, something that first Google, then CNF work hard at avoiding.

Another thing that might have been just me, but I really couldn't see any structure in Mesos deployments. Yes, you could run X, Y, Z on top of it to get various features, but they all had separate APIs, separate input files, etc.

Having used k8s before that it was a huge blow, since at the time (late 2018) I was used to think that Mesos et al were more mature and advanced, and instead encountered k8s circa 1.2 with less cohesion :/