IMO, most likely boils down to a few things:

-Lack of awareness, because the reddit protest was more of a vocal minority than a lot of people realized. For the mainstream crowd, even if people were upset, they didn’t care enough to actively search for an alternative. Even if they did, there were instantly a bunch of small team projects trying to bank on striking gold the way Reddit did when digg failed. This meant that support was splintered across multiple platforms and there was no post that even hit the majority of front pages or r/all that said “okay everyone, we’re all going to lemmy.world” or any other alternative.

-General confusion around the tech\platform and how it works. While it may seem to tech people that it isn’t any worse than any other site, just the concept of “picking a server” is a barrier to entry that makes a mainstream person think “oh I have to do research, maybe I’ll do this later.” I don’t know if this has been fixed yet, but as of a couple weeks ago there was some techy syntax to be able to properly link to content from outside servers properly if you’d viewed it and copied the link via your server.

-Older tech focused people tend to have self selected for caring about technical issues and searching for solutions to the issues they encounter. They tend to want control over their technology, and have it be open source or decentralized. The confusing nature of the fediverse is a lower barrier to entry for them.

-Performance. Performance was fairly poor at the critical moment when the apps got shut off, even if it’s improved now.

-User friendly dedicated apps that didn’t have a barrier to entry, like a warning that it was “early access” and granted devs special access to user data to help develop the app, were not available.

-Content. Because of all the aforementioned, there’s just not the user base and content yet to populate all the communities people want with enough fresh dopamine drip to grab all the mainstream lurkers. If Lemmy continues to grow and attract quality content though, there will eventually be a critical mass, because people usually go to what’s the new hip place after the early adopters have paved the way. Once you start getting a sizeable chunk of teenagers here and they start telling their friends “have you heard of Lemmy? It has less of that lame boomer crap” then you’ll see mass adoption. Alternatively, if the older tech folks end up just posting things that aren’t seen as hip\cool, that moment may not come.