In the best case, the community does pick up the work of patching and maintaining formulae (and casks). However, that's the best case, and low-volume formulae rarely fall into it.
In my experience, formulae tend to get abandoned by the upstream that originally submitted them, causing them to eventually break when the system or surrounding dependencies change. One potential solution is to have a chain of custody for formula maintenance, but that hasn't worked so well for MacPorts.
IMO that's self-inflicted by homebrew's policies. from https://docs.brew.sh/Acceptable-Formulae.html :
> We frown on authors submitting their own work unless it is very popular.
I'd expect "very popular" software to have relatively large populations of users capable of maintaining the formulae (and authors less likely to bother with packaging), while in lesser-known software, the respective authors are most likely to maintain long-time interest.
(It's pretty easy to contribute your own formulas, too! The checklist is pretty small.)
That said, I've occasionally run into a broken `brew cask install X`, so I get that maintenance is a thing. But in that situation it seems best to let someone else notice that and contribute a patch rather than remove it entirely. I understand that might eventually lead to a large percentage of broken casks though.