I think it’s basically recalcitrance. Same as they suddenly turn into the world’s worst devs every time they have to make software for Windows. Apple hates mouses, but many people won’t consider not using one, so they reluctantly make an expensive, pretty, and absolutely terrible mouse to get you over the hump of the macOS switch then keep pushing you along to where they really want you: the giant touchpad, where they do have a moat, and which trains you for the rest of their ecosystem. They even sneak half of that touchpad into the mouse itself, and half of the mouse out, so the transition is oh so easy.