Lemmy started for me in December 2022. By that point, I'd been on the fediverse for 6 months or so. The Twitter implosion had just happened the month before, and I finally realised how sick of centralised social media I was. Reddit was the only one I was using, though I barely touched it because of the moderation, and so I went looking for alternatives.
I found lemmy.ml, and saw the potential of the concept. A month later, in January 2023 my partner and I were running an instance (we already ran a regular fediverse instance). The lemmy instance was basically just a single person instance. Sign ups were open, but lemmy was quiet back then, so the few people that joined left again. My partner barely used lemmy, so it was basically a single person instance.
And then the reddit implosion happened, and suddenly we found ourselves running a fully fledged lemmy instance, with more users than our "main" instance. And that was really the moment that I got more serious about lemmy too. The increase in community size and engagement transformed the experience.
I've never been back to reddit since I left in December 2022, but I didn't delete my account until 2023 during the reddit exodus.