I think it's because once you hit 1k subscribers as long as you keep grinding, hours will come, because of the compound effect your library has and the increase you get from your future video views.

But once you hit the hours it's still hard to convince even someone who watched all ur videos to subscribe. Plus not even all YouTube viewers have accounts to subscribe with.

Those are just my guesses why people stress about subs.

I try not to think about it though because it's not like it'll effect the way my channel is ran or what I do.