I suspect there is a LOT of ‘vetting’ going on so that they can weed out potential spammers and autobots designed to crash the system
I am GLAD they are taking their time and not letting just anyone sign up.
Parler had (or maybe still has) that problem- each post would immediately get dozens of spambot messages in the comment section. It made it unusable.
But it's more than that, I think. People are genuinely interested in networking. I suspect that there will be future enhancements that would, for example, allow users to find other user accounts in their Congressional District.
That is one of the reasons a follow-back culture has taken hold. Reciprocity is a pretty big deal. No one expects Don Jr to follow back, but they certainly expect Joe Blow to do so.
A "follows you" mechanism is soon to come into play so people can identify which of their followers didn't follow back, and can decide whether to keep following them or not.