I found a discussion on some crappy Lemmy clone. It's really tedious. The TLDR seems to be he promoted a tool for blocking Twitter accounts back when gamergate was a thing, then when he joined Mastodon there were some former Twitter peeps who'd got blocked and were still mad about it.

@bloopernova @fathermcgruder this is the short version of why: https://old.reddit.com/r/OutOfTheLoop/comments/9bimug/why_did_mastodon_run_off_wil_wheaton/e57gknd/

Probably people who love Star Trek but hate The Big Bang theory. Could be the other way around too I suppose.

@bloopernova I don't remember what people were annoyed with him about, but I do remember that it was a BOFA joke that was the last straw for him. Anyway, he's the only high-profile Mastodon user that even comes to mind.