Lemmy wasn't ready and still mostly not ready for a mass Reddit exodus. The Reddit API fiasco wasn't anticipated by anybody and the large influx of users exposed a ton of bugs and federation issues.
But it's not a failure, yet. I'm sure Reddit had growing pains after the Digg exodus too. Some platforms take years to become popular. Reddit was small for quite a while before it became more mainstream.
In a way to me Lemmy feels a bit like Reddit must have been a few years before I joined it 12 years ago.
The problem is the expectation that Lemmy could replace Reddit overnight, and would immediately be a 1:1 replacement.
Although personally I like it more here, and I get more interactions than Reddit. But I am a tech nerd, so.