What kind of chaotic world would we live in if you could put third party paper in your Smith Corona typewriter? Think of the security risk and how much it would confuse people! And it's their platform...they deserve a cut of any commerce performed using it. /s
This is why I find the idea of Apple making an electric car so intriguing. It opens up a whole world of possibilities for things that Apple can take a 30% cut of: anything you buy at the supermarket, any clothes you buy, etc. If any store doesn't allow Apple to audit their sales and pay the tax, your Apple car simply won't go allow you to go that store anymore.