Right there is inherent inertial momentum with upvotes.
I'm still on the fence, because understandably the potential (and actual) for abuse makes downvotes very unproductive as a feature, but there are also situations where they are very powerful.
It takes significantly more effort to refute a wrong position than it takes to make it. Downvotes serve as an explicit balancing point against that in ways that a well written response does not. Additionally, nested comments usually get less upvotes than their parent comments.
It is what it is I guess.
The "numbers" are called Discriminators and served a variety of purposes:
You argue that being able to use effectively the same username everywhere is a good thing. The unfortunate reality is the rollout Discord used alongside the limited number of permutations (combinations?) of short usernames makes this impractical. For example, a friend largely goes by a 4-char username, and the switch by Discord means they can't use that 4-char username on Discord anymore. It's easy to say like "well, just add something to the end", but that is exactly what discriminators did.
At the end of the day the benefits weren't as compelling as the losses (it would suck to have one's identity impersonated or username stolen, or now most folks with short usernames have to stop friend requests cause they are getting spammed with them, or the fact these accounts are valuable and can be sold).
It is understandable that some people don't really care about the matter and that's fine, but it doesn't make the frustrations others feel less important.