They got an influx of exodus like a week ago but stopped accepting new users because their server couldn't handle the huge communication. In contrast, kbin.social continues to accept new users, who might be more active than who joined a week before.
This might explain the difference. Or that pro-CCP behavior of Lemmy devs pissed off Lemmiers.
That Lemmy.ml is the main instance and I read that the Lemmy devs themselves are tankies. I didn't choose Lemmy because I wanted to minimize my contribution to these people.