I came too because off the newest anti user behavior of reddits CEO and Admins. Made an Account on feddit.de and now have access to all Communities in the Fediverse.
I was using Infinity for reddit most of the past years and would not switch back to the awful reddit default Android App.
The official lemmy App is not perfect. But all ready good enough to be used with mostly no bigger issues. Mostly lacking in some features compared to infinity.
It likely is spam/bot accounts. Multiple admins of instances with open reg have commented/posted about having to fight bot sign-ups the past few days. The only fix that helped (they said) was to enable captcha. There's a git issue on the lemmy project mentioning that they are removing captcha, so the admins are particularly worried about that...
It's definitely mostly bots. There's over 1 million accounts over all the instances now. I think out of a prediction maybe somewhere between 200k-400k are actual users. The rest is just bots plumping up those numbers.