Ultimately, it's the lack of any real reason to use it.

As a user, there's no content on any PeerTube instances that I'm particularly interested in. Or if there is, I have no realistic way of locating it because the search/discovery features are effectively non-functional; unless you're really into 3-hour videos titled "A Deep Dive into Every Reason why Richard Stallman was Right", the recommendations are otherwise useless. There's also no features that interest me that aren't also available on any other platform I consume video from.

As a small creator (under 500 followers across 3 platforms), there's no audience to show my content to on PeerTube, and no real way to gain an audience. There's effectively zero exposure opportunities on PeerTube, and unless you already have a large audience that you can convince to move to a new platform, then nobody's going to see your content. Even though I'm not making videos for any monetary gain and doing it purely because it's fun for me, a big part of that fun comes from the engagement I get to have with the community. And if that community isn't going to be active on PeerTube, then neither will I; this was the reason I stopped posting to Loops.

If I were a larger creator, or somebody whose income relied on video creation, then I would have even less inclination to use PeerTube because the monetization capabilities are basically nonexistent. Yes, you can add a KoFi link to your channel details, but you can also draw a QR code to your KoFi link on a cardboard sign and stand by the traffic lights for all that's worth; in fact, I think that would actually still give you MORE exposure than PeerTube would, and you don't even have to make videos to do that.

While I generally agree with the ideology behind PeerTube and want to see it succeed, it's just not in any practical state for me, no matter which angle I look at it from.