Proton abandoning Mastodon because of "lack of resources" sounds to me like a shitty excuse. Mastodon is probably where they get the most tags for their recent CEO moves so it's just easier to ignore the users on Mastodon and "nurture relationships" on platforms where they won't be held accountable.
edit: Thanks to someone pointing out this post with their follower count. They left the Social Media where they had the MOST followers