In theory, I agree with you! A 100%, but the problem is that currently Lemmy doesn't support migrating your profile to a different server. So that already slightly complicates things. So from the get-go they are forced to make choice. A choice which isn't clear, what potential consequences are and the fact they currently easily migrate to a different server, obviously doesn't help.
"Like email" is basically the same description I've been using to explain it to non-tech people.
Long story short, onboarding needs to get better. But that also applies for other Fediverse projects (like Mastodon or Friendica).