I wonder what it is that is keeping more diverse users away?
I know what is. It's the instances concept and lack of mobile apps. Sure you can open the web page in any mobile browser and it will render fine but just the amount of instances, their specific rules and perhaps many people not realizing you can connect to other instances is one of the biggest drawbacks even if it's the most powerful feature of the Fediverse.
Reddit is a single site, single brand, single point of contact. For Lemmy it feels like many different sites using the same template but with their own communities that other instances also have so users might get confused by the whole concept.