That's a strange read on Reddit. I've heard people say this before, and it's baffling.
Reddit is, and always has been, a link aggregator first and foremost. Of course it's reposts and screenshots of others sites. That's kind of the point. To bring you Twitter so you don't have to actually be on twitter.
Not to mention a supermajority of reddit users are inactive. Recap has shown that even with minimal activity, you end up in the top 1% of reddit users.
That means reddit has roughly 5 million active users. Meanwhile nearly every person that creates a lemmy account, is active too.
A couple of years ago I ended up in the 1% because of one single thing I posted 2 weeks after I signed up purely to generate some rage because so many subs needed minimum karma... Can completely attest to this.
I suppose this is related to your “users are inactive” point but I also feel like it’s more common on Reddit to have multiple/alt accounts. Hell, in my time on Reddit I think I made 7+ accounts.
Why? I feel like that would be more common on Lemmy than anything. There is an actual point in using different instances here, I don't see any point whatsoever on Reddit.