Being new to Mastodon and Lemmy I personally struggle to figure things out.
Just finding a brief summary on how Lemmy works in contrast to reddit has, so far, yielded no helpful results.
While I think for me this is just a matter of sticking with the services I can imagine that a lot of people would check in, struggle and check out again.
The, let's call it infrastructure, of Lemmy and the way registration works due to the fediverse is quite different to what most people are used to.
For me it's the lack of content that is killing Lemmy. It's just not nearly as entertaining here as it was on Reddit. I know the community isn't the same size so it isn't comparable really, but it's just the same content here day after day.
It is against the idea of the fediverse, but if you point a new user to a general purpose Lemmy instance and tell to sign up there, there isn't much difference to reddit?
Default to the all communities feed, a single sign in page and they're good to go.
I agree that the basic functions are similar, comping one particular instance of lemmy with reddit, but the fediverse, at least in my opinion, adds to the complexity. And when it comes to complexity, you have to keep in mind that there are business models out there focused on reducing the complexity of much more basic needs such as preparing a meal.
What if the instance I have registered with doesn't provide a particular content I crave? If a new account was required to get the content I'm liking for, it may be a deal breaker. This problem is solved elegantly by federation. But if I browse all to search for that particular sub(?) which one ist the right one?
There is (at least for a newcommer) so much choice (compared to reddit) which looks very similar at first glance. Choosing a sub or an instance is not complicated, but in it's nature complex, and the ability and willingness to handle that complexity may be major turn off for many newcomers.
I saw someone post that the competition between subs on different instances would drive quality, but that is not necessarily the case, when the metric I use is the number of followers in a sub. In the end, this thought of a free market will either result in a monopoly, one sub on one instance being preferred due to the amount of content and hence the visibility, or stagnation because none of the subs will provide the necessary quality to attract the masses.