Gaga announced a tour which did a lot better than we expected back then, and that is the most profitable thing she could do. And releasing new music so quick would have been a little awkward imo, she needed to push Joanne and MR once more and it was proven to be worth it.
Edit: jfc Gaga has definitely missed a lot of oportunities and it is kinda frustrating for us, but I dont think that was one if the cases