Registering for a website is not something most people find so mystifying. Short of being willfully obtuse, I would imagine most people who express discontent with online communities could exert the most cursory of efforts to understand how to do it. Typically it involves visiting a URL and then typing in an email address and a password. Please pass this on if you come across anyone struggling to comprehend it.
Getting into a federated space brings a lot of questions for normal people. Why this instance? Why not this instance? Can I only join one? What if my friends join a different one? This one only has 100 people, is it weird if I join? This one has 1,000,000 million, isn't that basically Reddit/Twitter/whatever?
These are the sorts of questions that come to mind for normal people. By the time they've asked this pile of questions they've already decided it's not worth the hassle of finding the answers
As people positioned to understand this stuff, we have a duty to explain it to people if we believe it will have a positive impact on society. I'm not oblivious to the fact that lots of people have lots of questions about decentralised social media, I'm saying the answers can be very simple. That should be enough to realise that the fatalism some people seem to experience in the face of this new technology only exposes their own intellectual laziness -- not the confusion of "normal people" and not the insurmountable complexity of that technology.