I think you are confused. I self-host a ton of stuff. One thing I have zero interest in is hosting mail and dealing with all of the configuration and possible timebombs waiting before I can even do the single thing I want the service to do. Instead I pay like $5/month for essentially unlimited emails from any domain I control.
That said, none of it has to do with my own personal email, which has been on Gmail for long enough to drink, so we are probably talking about two different situations.
I think the label "self-hoster" might be overly broad in these sort of discussions. Some people considering firing up a VPS and running something like Posthorn "self-hosting" email, just like a bunch of "modern" AI tooling says "local-first" because the CLI runs locally, although all LLM models are remotely called.
Seems to me like there a broad spectrum of "self-hosters", ranging from "I run everything on my hardware in my home" to "I deploy FOSS SaaS software to AWS for us to run", probably neither of these are more/less "self-hosting" than the other.