Yeah, if Apple Pay and Google Pay has the same market share then website could integrate those service and achieve the same, I agree. However, Apple Pay and Google Pay are also harder to use from the perspective of both consumers and merchants in these countries in the beginning, and IMO that's the reason they failed in the first place.

I don't know what payment methods these services require now, but in the beginning at least, they both supports just credit cards, which is basically suicidal. Most users won't be able to use it at all.

From merchants' perspective, they don't need to pay for transactions on WeChat Pay or AliPay, whereas both Apple Pay and credit card companies would charge them for usage. For this reason most small business wouldn't even think of using them.