It's at the top of the list on join-lemmy.org's popular server list, next to lemmy.world and beehaw.org, of course new users will sign up on the more popular ones. Plus, a few posts on reddit called out these three which set everything in motion.
Once folks start to understand how it works, they might start to sign up on other ones, for a "cooler handle @ address" for their user, or register a domain and start their own instance like I did.