I am not defending Apple. I think Apple's behavior here should be illegal. I am merely stating what warped logic Apple seems to be locally applying here based on my understanding of the situation, from the perspective of their ludicrous, vague, and inconsistent policies.

E-commerce presumably falls under “physical goods” in Apple’s eyes, which is allowed.

Which seems rather arbitrary, it's not like you can't buy digital goods from Steam over the web.

This is yet another reason we must fight these proprietary app walled gardens. It's a clear regression from the open web.

For a while, you couldn't have Steam Link on iOS because it would be "bad" for Apple if you did buy a PC game through a live stream of your desktop.

https://9to5mac.com/2019/05/15/steam-link-ios-launch/