That, and for Lemmy specifically, its history of being a tankie forum. Without the Reddit refugee migration, if you joined Lemmy as a single user, you would be alone among communists and eventually get bullied into leaving. Already in 2020-2021, Fediverse users knew about Lemmy, but they avoided promoting it because of its userbase. This Reddit situation provided the push to get many normal users over to Lemmy at once to drown out the communist users.