First, if it helps, redundant communities will solve themselves. We’re in a period where people are trying stuff out, but if one group is just a weaker duplicate of another, everyone will eventually just coalesce around the slightly better version.
As for the general complaint, I can see your rationale. But I think a better analogy instead of cryptocoins – which were all essentially useless ponzi schemes and ego projects – would be bars.
In theory, you don’t need two (or more!) sports bars on the same block. But there’s a reason they stay in business instead of one owner just expanding to serve twice as many customers. They have different vibes based on different people. One might dig soccer more, or have a better selection of craft brews. Even though they’re superficially similar, if you ask your friend, “Hey, do you want to go to X?” It’s not at all weird for them to say, “Eh… let’s to Y. if you want, we can stop by X later.”