This is not a car, not an electrical outlet, nor a food processing plant, where some standards should apply. While all companies have to follow current laws, mass produced products intended for consumer consumption in competing markets differentiate themselves by the features. Nobody is forcing consumers to buy the products. And if one doesn't like the features or doesn't thing the value to price ratio is right for them, move on. And if one believes the manufacturer is limiting the choices of customers, buy another product that doesn't. Really quite simple.
I appreciate that we will probably never really agree on this because we come from completely different perspectives. I simply don't believe that mobile phones are -- or at least will be -- just pieces of consumer electronics. They are increasingly the main or even the only way people access all sorts of things, from the mundane to the very essential. They connect people, they are how people increasingly buy goods and services, use services, do their banking etc etc. That's great, nothing wrong with that.
Because they are increasingly becoming so essential it's simply not desirable to enable any one company to use its position as hardware or software platform provider to privilege its own services over those of others. It's simply not healthy. Equally, there is no good (public policy) reason to expect people who might want to use a different payment provider than Apple Pay to have to change their entire ecosystem, nor is it likely that a lot of people would do so.
From the perspective of a market regulator it is therefore probably not very convincing to rely on consumer choices as the only vehicle to ensure effective competition in your jurisdiction. If you have an iPhone you are likely to use Apple Pay because that's your only option other than throwing out your iPhone (and potentially your Mac)?
Additionally and unrelated but related after all, a frequently heard argument is that competitors should simply create their own platform if they're not happy with Apple. This is even less convincing not just because there's probably not a lot of room next to iOS and Android, but more importantly because to suggest every service provider needs to create their own hardware platform because or in case the big platforms have shut them out in favour of their in-house services is ridiculous (not that you have made this suggestion here, but some have in one way or another).
All of this, of course, sucks for Apple who have created a very successful platform and now want to capitalise on this platform through other services they can push through it. That's understandable, but probably also undesirable in the broader picture even though individual customers may appreciate the coherent service Apple can provide them. Yet nobody has suggested that Apple would no longer be allowed to do that, just that Apple needs to compete on a level playing field with its services. They might still be better and customers might still choose them, I certainly would in a lot of cases, but we don't want Apple (or others) to corner certain markets by default.