I think a problem for new users is failing to understand how the Fediverse works. It’s not something apparent and not something you can expect everyone to understand right off the bat. A user may start out on a heavily loaded instance and get discouraged by poor response. They either figure out they need to find a better instance or base their opinion of the whole on that one experience and give up altogether.

Lemmy.ml and lemmy.world can suffer from heavy user load and bog down at times. That situation can be avoided by selecting an instance that’s not too heavily loaded. There’s a large number to choose from. It may be necessary to shop around for a good one. In technical terms, find a regionally local instance with low hops, fast ping, and good server response. Also admin settings and quality can be a consideration. I actually signed up on four instances before I found one I really liked.