I'm the same, more specifically, Kubuntu, I love KDE Plasma but I can't deal with Arch/Fedora lack of stability, hence the recent Fedora mesa driver breakage and all. I can't get enough of Ubuntu (Kubuntu), it is simply the best middle-ground between stability and fresh packages, especially if you don't stick to LTS. While other distros often have issues, the interim releases are rock solid, they are up-to-date enough that you don't feel left out of a cool feature.

As of now, Arch/Fedora ship with Plasma 6.5, while Kubuntu 25.10 is still on 6.4, and I'm glad they choose to do so because I had a ton of issues with 6.5, it crashes A LOT. While Kubuntu is rock solid, zero issues, and uppon next release, 26.04, I'll have a new Plasma to be excited about. This is good practice imo, not to ship the very latest of the DEs, since it gives it better stability, hence my experience atm. Not to mention that it gives you enough time to appreciate things, while in the Fedora/Arch land, you get updates so fast that you can't even properly use things, and out of nowhere, you are getting a new version.

I also tried a shit ton of other distros, and the number 2 reason why I also get back to Ubuntu is compatibility, same as you. I lost count on how many times I had to look into documentation on how to build from source, or there was simply no documentation, while Ubuntu was forever covered and supported. It is is nice to not have to think about whether if my distro will be supported or not because, lets face it, Linux is already niche enough, not using Ubuntu is even more niche. One distro that I really tried using was Debian, because it is Ubuntu's base, but still, most things still expect Ubuntu and not Debian, so it is not a 1:1 thing, you still get some friction, just less than on Arch/Fedora.

And ofc there is also Linux Mint, I'll admit that if Plasma wasn't so great, and if Cinnamon had proper Wayland support, then Mint would be my forever distro. It is simply amazing, up-to-date enough kernel, GPU drivers and always the latest Cinnamon, they just need to figure out Wayland and it'll be perfect. Another one I loved using was Fedora, I was quite a big fan of it, but I get annoyed on the lack of 3rd party repos for things, same old story of Ubuntu being the only distro some companies think that exist. Not to mention, as already said, I think Fedora updates too often, almost as often as Arch in my experience.

So there you go, you are definitely not alone, most people, even in the Linux ecosystem, don't really put much thought on what OS they are using. And this results in Ubuntu still being the most used distro, even to this day, but I really think that SteamOS will be the number 2 very soon when the Steam Machines launch. Lets be honest, most people won't change SteamOS from it similar to how it is used on the Steam Deck, at least I'm one of those people, it just works, I use it as a computer, even with my development environment containers using Podman, it is simply good enough. I think the main expression here is "good enough", Ubuntu is what it is because it is good enough for most people not to care for looking elsewhere.