Hmm, it didn’t used to require an email address but it appears that now matrix.org does. It may be a spam-fighting measure because they have had a lot of trouble with that in the past. …not that a email will do much.

You can try finding a different homeserver that doesn’t require an email address to sign up (or run your own if you are ambitious).

Here’s a list of other homeservers: https://tatsumoto-ren.github.io/blog/list-of-matrix-servers.html