Aside from being a difficult concept for non-tech people to grasp, the problem with the fediverse is that it’s an absolute nightmare to moderate. Nothing is stopping bad actors from creating their own instance and flooding others with illegal content. Lemmy World and Lemmy.ml have already had incidents where communities have been targeted and flooded with CSAM.
Social media platforms that I do have problems with can’t see a good fediverse alternative for these reasons, plus a few others.
YouTube as one such example: the problem is that video hosting costs a lot of money.