Because 99% of helfhosters pull containers, with zero understanding of what they do. They they try email, because heck why not also email, and hit the wall of actually must understand what you are doing or else...
Yes probably selfhosting email is for advanced users, people who at least know how to manage a DNS record and how nwtworking works. Maybe it's just that selfhosting bar has dropped significantly thanks to docker, and indeed email hosting is a bit more complex that just "docker compose pull" approach.
Yet i think people should not be scaring others so easily on email self hosting, it's perfectly doable and fun to do. Maybe don't switch your primary account just imediately to mitigate risks...
Isn't that the gist of selfhosting?
Yes you can do it, yes you can have it done for you by somebody else. The first is fun, and risky, the second is less fun and less risky. We are all here for the fun... and probably we all don't care too much of the risks. But why shut down everybody who ask about email selfhosting with a don't do it? Let them try, make errors and fix them, maybe they learn something new, maybe it works out for them
What is the worst that might come out of it? Some spam? A blacklist? Come on, you can survive both. Don't use your primary email account as self hosted from the beginning maybe, to mitigate all those risks, no?