Honestly just inertia. Those are not servers (where you could easily migrate to another distro taking advantage of infra-as-code tools), they are a desktop and a HTPC. I have accumulated a lot of custom dotfiles, Ubuntu-specific utilities and scripts over time, not all of them would work in another distro unchanged.

Removing Snap is not that hard, the "hardest" part is making sure that Firefox is installed from the Mozilla PPA and even that takes just a moment once you have the script saved somewhere.

By the way I had a look at some Ubuntu derivatives like PopOS or Mint and I might take the plunge at some point.