That’s really bad if discourse really stands for openess.
If you follow the recommended install guide and use one of the recommended mail providers Discourse installs without problem.
If you step outside those recommendations the assumption is that you’re capable of adapting to those changes.
If you don’t want to do (1) and can’t manage (2) that’s precisely why hosting options exist. It has nothing to do with openness and everything to do with technical competence.