Because you cannot own or operate a cellphone. The cell phone modem is not licensed or controlled by you. It cannot be, it is the telecommunication company's. And this reality is intruding more and more into everyday life. You will not be allowed to control your smartphone. They are terrible computers because of this. A smartphone's legal purpose is now basically just banking, shopping, and navigation. Other things that interfere with commerce will not be allowed.

Just use your phone as a hotspot with a real computer for computing that you can and do own.