It quite literally is forcing you to use it. Downloading via NMM no longer works. It defaults to Vortex and to even use NMM, you have to manually download the mods then find the files via the "Add File" function. If we "moved" them, it would break your NMM installation and you would not be able to go back to NMM in case you don't like it. I don't think that is a good idea. Why not allow Vortex to use the same directory or something. It's a huge hassle for people with large amounts of mods to have their mods copied and pasted into a new directory. Not only would it take a hell of a long time to do; it doubles the size you invest into your mods.