I think it really is about looks. It streamlines the look of each video info so it doesn't matter if you have 354 subscribers or 35,427,298. Also if you go to the youtubers homepage you can still see the accurate count.
But if I own a 35.427.298 subscriber channel, I would prefer the majestic full number to appear. Same for views: 1B nearly looks like 18.
Also, no, the public subscriber count has been abbreviated entirely since late 2019.
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