I still use Reddit, but less after the API changes. I was already using Mastodon and aware of Lemmy when that happened, but the biggest server previously was lemmy.ml, and even that wasn't very active. I put it in the back of my mind to check on again in hopes it would gain relevance. Reddit pissed off a bunch of its users, so it did.
Lemmy.world launched around then, and I'd heard of its admins by way of their well-known Mastodon server so I signed up.