You don't think it's worth it most the time because of the hassle of setting up and managing a cluster, or because clusters in and of it self is not necessary for most?
The latter. I think it's a 1% business case, basically. I mean, if we can get 80% benefit without excessive cost, then it's obviously a good idea. (And I do use Ansible/Docker and the like, but it's not entirely without friction... which is where the cost/benefit analysis comes in.)
EDIT: Obviously, if you really need clustering, then you need it, but IME people tend to overestimate their needs drastically. Everybody wants to be Big Data, but almost nobody actually is.
In a perfect world everything is cluster-ready &c at the outset. In this world it usually... isn't.
EDIT: ... and I'd posit that such cluster-readiness actually isn't worth it most of the time.