For a FOSS project targeting people who are comfortable using FOSS this seems entirely fine...desirable even. "We don't have money for phone staff who would put you on hold and only be reading off scripted responses anyway, but you can come chat directly with the leaders and maintainers of the software by chat".
I'm a part of a few Discords, and questions are repeated over and over again, forever. People who answer the questions, get tired of answering the same thing and eventually stops helping people. In contrast, using Stack Overflow or anything else, people can search Google for answers and actually find it.
Edit: Misheard parent...
to my knowledge, this is is only an optional moderation feature on some servers, not a global policy - you can still use discord without an email address if the server rules are loose enough