This is pretty much it - you nailed it with repetitive bullshit. We've been over all the causes before, many times - He's constantly rehashing the same points without any care to introduce them to 'new' viewers, he's always late on the ball, he looks more and more clownish, he's become more condescending and insulting to his audience as time has gone on, and he's never made an effort to improve or evolve his formula in years. Here lies dying brand, Jim thought he was hosting the funeral, but its actually for him.
Even if someone doesn't nope out of the troon saga, other creators have gotten better while he's declined, and people don't usually like to watch the same video three times over. If you watched any other person talk about the news the day it became relevant, then any take Jim has will be a week late, and a subset of what was already said - never additive, never unique. People stop watching, and eventually unsub due to youtube homepage behavior - If you are subbed to someone, it will keep their newest videos in that homepage until you watch them, clogging up the feed. There's other ways to clear it out but most people just know that unsub will do it.
If channels like Cooking with Jack are any indication of the zombie floor, its gonna be around half a million or less. Both are fairly old youtube accounts which gained early popularity and then went to shit. While the hardcore group is probably around 80k based on Patreon numbers, and declining. He could legit floor around 500k, and that's assuming youtube doesn't aggressively increase their clearing of zombie subs.