And it’s not like Apple violated Xerox’s patents. (Or did Xerox never patent their GUI?)
Off the top of my head, I don’t think Xerox ever did patent their work on the GUI, for several reasons. Software was not generally considered patentable at that time, and certainly general concepts like the desktop metaphor, GUI tool kits, etc, weren’t. Also, IIRC, I believe Apple actually bought some of this technology from Xerox. As I say, though, that’s purely off the top of my head.
I thought there was some sort of stock deal at the time Apple looked over Xerox's work. I could be wrong, though.