Think about things from the point of view of someone who has never used Reddit or the fediverse, but you've heard about them both from recent news articles and want to see what they are about.
Reddit:- You Google Reddit and your first result is Reddit.com. You click the link and are presented with the front page. You from scroll from a few hours and end up signing up and staying.
Lemmy:- You Google Lemmy and your first result is a wiki article for Lemmy Kilmister... Your second result might be join-lemmy.org, which you're smart enough to realise it's probably more likely what the news is about.
You click join-lemmy.org and are presented with a page of information about the fediverse, links to set up a server and pictures of code...
There is very little chance you're going to investigate further.
If we want the fediverse to replace Reddit then either
A) Lemmy needs to improve its initial impression and Search engine optimization
B) We should be promoting a different platform with a better initial first impression.
I'd recommend kbin personally as it gives the same sort of experience as Reddit from the initial interaction.
I do like a lot of things about Kbin, and visually it's much better than unmodified Lemmy in a browser, but it also has its own share of problems, not least with intuitiveness. I don't understand why communities are called Magazines, and the terminology of "Favorite", "Reduce" and "Boost" are very confusing to me. Trying to make a new thread might lead you down a microblogging path instead since "Post" sounds more like a new thread than "Article" to a newcomer.
There also seems to be much slower sync between Kbin and various Lemmy instances compared to intra-sync between lemmy instances themselves. Kbin also doesn't have an API (yet?), but a more tech savvy individual than me will have to say how big of a deal that is.
Both Sync and Boost have large and loyal userbases and will probably attract plenty of users to Lemmy, and good Third Party Apps might help with first impressions and onboarding for new users.
Ultimately though, content is king. I liked Kbin better when I first made my accounts, but then we had a Race Week in Formula 1 and the community here was dead while discussions were happening on Lemmy, and since the sync was slow so I ended up over there.