I didn't care too much about API changes at first - I used on open source app on my phone but mostly browsed desktop. Would have been fine going back to desktop only. As long as they keep the old site design around, I'd be fine to stay.
What killed it for me was the absolutely un-caring, not-budging response from leadership. I don't feel good continuing to feed the site my attention at that point.
I like quirky Foss stuff anyway, so I was already curious about Mastodon and Lemmy. But I'd always figured they'd be ghost towns. Twitter and Reddit deliberately being proudly, blatantly awful was enough to push me out to here, along with enough other folks.