Now imagine someone makes a program that repeatedly installs and uninstalls the game. They let this program run all day every day. They also give the program to their friends or post it online.
Unity says they have measures against this, but that then smells of spyware. How would they know how many times a game has been installed without that?
Unity may say they have a solution to that too, but no matter the implementation, bad actors will find a way to exploit it.