As a customer, if I consider Apple Pay so much more convenient, I'll choose a bank which supports it. So banks are under pressure to either support Apple Pay, or create an equally customer-friendly offer.
If I consider another offer better for me, I will use their App instead of Apple Pay. So Apple can't just enjoy their monopoly, but is under pressure to be the best option for customers.
It’s most certainly not that simple. Anybody who wants to is free to compete with Apple, and many, many companies already do. But this is legislators dictating what 3rd party software Apple must support in its operating systems. Why stop there? Why not force Apple to support 3rd party providers as an alternative to iCloud? Why not mandate a 3rd party App Store? Why should Apple be allowed any control over which operating system or hardware features it exposes to 3rd parties at all? Why should Amazon be allowed to ship a kindle that only supports their book store?
And indeed, why not doing this for other closed ecosystems as well, if this is beneficial for the public?
If public benefit is your only concern, then why don’t you consider the benefit of closed ecosystems, or at least of consumers having the option to choose one? I don’t see any public benefit in removing options for consumers. If open ecosystems offer such a superior benefit to consumers, then surely they would be able to out compete closed ones.
Also, it needs to be balanced with the interests of the companies owning the ecosystem.
So it would be your turn now to argue why this specific law is harmful for the public. (We agree that it is harmful for Apple.)
How is it obvious? One could easily argue that because some hardware manufacturers make shitty drivers, opening up access will allow 3rd party developers to create better drivers, or something like that.