I understand you're specifically talking about Apple Pay, but the same logic could be applied to iMessage.
Do you feel that Apple should never have bothered to develop iMessage because not everybody has an iDevice?
It would be nice if all chat clients talked to each other of course, but at the end of the day it's just "chat" and we have many ways to communicated.
The transfer of goods for currency is basic and fundamental to how the world works in reality.
You have goods and I give you currency in change for those goods.
To make this work we invented the thing called "Money"
And it needs to be standard to work.
I'm all for any advancement, but lets look at the current method/s and come up with a new (better?) method, easier to use that also works for everyone.
Having incompatible money does no one any favors, as you then have to also carry other methods in case the person you wish to buy items from can't accept your form of payment.
It would be like having the USA, and having 6 foreign cash currencies live in the USA at the same time, and any trader as any location could pick which of them to accept or give out.
What a nightmare that would be for you as a consumer.
You would be saying. For gods sake, lets all use the same one so I don't need to carry all 6 with me at all times.
So, now, in this "Modern World" we have the knowledge and skill to make sure we don't mess up and we work FOR the consumer, and all tech companies work together FOR THE GOOD of the consumers and set a standard that they are all compatible with.
Sure they have can their own user interface or perhaps security that each device needs in order to activate this function, but once set up on ANY device, the actual transfer and ability to pay should be 100% compatible with a standard.
So I can order my Tesla Car, Buy the burger, Get a stick of gum, Pay you $1.13, buy a plastic toy from a yard sale, etc etc with the same method, and everyone with any "phone?" can accept the payment. from 1 cent to say $100,000.