According to this question there are three reasons to ban someone from making tag edit suggestions and two of them definitely don't apply:
because a large number of recent suggested edits by you were rejected - Doesn't apply; I haven't had any suggestions rejected at all.
you triggered the anonymous insta-ban filter - All of my edits have been logged in. None are anonymous.
That only leaves
- a moderator manually banned you
or the possibility that there's a 4th reason not given in that answer. Does anyone know why I can't propose edits?