I think the idea is rather that you would set it up on your own host. What you're mentioning could likely be alleviated by a properly configured caching reverse proxy.

maybe

a lot of backend software doesn't provide cache invalidation signals

a lot of caching reverse proxies don't support cache invalidation, or don't support it efficiently

you can't always prerender all possible views

and this is the kind of situation where a slightly out-of-date page could be a huge hassle or even cause a major outage; imagine pushing a branch to production because you thought it didn't have your latest buggy commit in it

it probably isn't going to be any faster on my own host