I'd like to add to all of the reasons I find valid (not obscuring what one is pointing at, mimicking pointing with a finger) that everything displayed on the screen is pretty much perpendicular to the x or y axis. The tilted cursor thus sticks out among the rest of the content. As an aside, as a typical Amiga quirk, the early Amiga mouse cursor was tilted in a 45° angle to the x axis, contrary to all the other popula…
Similar to the Macintosh mouse pointer the click point was not at (0,0) but at (1,1) (the orange point in the skin colored area in the editor on the linked page).