Legacy reasons I suppose, it would suck to go back to a photo you took a while back, only to find out all your edits are gone because the modules you used are removed.
Some modules get a “deprecated” warning, which imo more modules could use, but there are probably still edge cases where someone might prefer the old modules
I think they are hidden by default with the scene-referred layout, but they will show up when searching. It’s a tough situation UX wise