It is simple: nowadays security awareness is drilled in for most of the online population. If presented with a choice people can't oversee, the default safest option is not to chose. I mean, how many new Mastodon users know any of these servers?

So, as couter-intuitive or even ironic it may seem, the "problem" is choice. People need to learn that social media is no longer a single entity, but more like email or choosing a bank.