There are 100M+ channels uploading on YouTube regularly and only 2-3M of them are monetized. Not everyone wants to upload videos on the internet with the explicit goal of making money. Professional creators are a very tiny minority, and a platform like YouTube will always be better suited for them (your "small" channel with 100K subscribers is actually in the top 0.5-0.1% of YouTube). There is no reason for Peertube to go after this specific demographic.
Yet those 2-3M channels get the lions share of the views. It is a two-sided system. And if you want to attract viewers, you need what they want to watch. Looking on the front page of peertube the most viewed video I see has 29 views. If I sort by hot, the "hottest" video has 692 in a month. If the intent is to publish videos to have people watch it, PeerTube is clearly not the place to do that.
If you want real numbers start selling hard drugs. You don't have to "serve the people". YouTube is a cesspool.
Then there's even less reason to host outside of YouTube, why would I want to host a server that costs money if I'm not making any money from the videos? It works for those who want to own their content and verify its safety, or for ideological reasons such as supporting OSS but I'm not sure why the average user would care about PeerTube.
The problem is that big creators have many subscribers, because they're the only ones making videos people want to watch.
If a channel has 100 subscribers - (except if it's a brand new channel) - it's because people saw the videos and decided, no, I don't want to see this, I'm not going to subscribe.
Put all of those people on a platform together, you will just end up with a platform with more creators than viewers.
So? Why is that a problem? My wife occasionally watches this old lady who's vlogged every day for over 14 years straight. She averages 150-200 views. The people who try to build a brand end up getting outsized attention so it seems like that must be what anyone would want, but most people actually aren't trying to do that.
Well, do you want a platform people watch videos on, or a platform people simply upload videos to, never to be seen?
It's not an either-or, but generally speaking, a platform centered around getting more people to watch is probably worse to have in the world than one centered around people just expressing themselves to a handful of e.g. family/friends/small communities. Especially if the former is really just a conduit for ads.