How are plural names linked to those things, though? I have a low-care level for naming conventions so long as there are conventions. Many successful frameworks use plural tables names. Though I agree singular probably makes a little more sense, especially since it eliminates the need for inflection code.
Your UserRegistrationService(s) is/are also prone to be overloaded. You don’t think of that as part of a naming convention? Would you argue that’s more about architecture? I was simultaneously agreeing with you and adding that this other minor organizational annoyance I have adds to the pile. Apologies if that seems low value.