You cant force a seller/company to accept every form of payment or payment processor. Especially one that takes 30% cut, and says they cant sell their goods themself to people (aka sideload).

Not only does such system seem insane for a normal payment processor. It also effects you the purchaser in multiple ways. Since to use this payment system you cant make the choice to buy anything but through them. It also prevents in you from fully owning your own hardware.

So the end results they force both developers and users through them. I find the effect of not allowing side-loading even more egregious because once apple sells the phone they no longer own it.