I've made many ApplePay transactions. I've had a few terminal failures, but mostly the problem is: it just doesn't work the way it was promised to work.
I have a debit card linked. (I don't have any straight credit cards.) I have never been able to simply tap the phone and do my fingerprint to pay. I have had to enter a PIN, give a signature, answer questions about whether I want cash back or if the amount is correct, etc.
It's so universal that I actually went back and watched the keynote again to see if I had imagined the part where they showed checkout with just a tap and fingerprint, but that's exactly what they showed.
With all those extra steps, ApplePay provides only marginal utility. If I'm paying with ApplePay, I don't want cash back, I shouldn't need to sign or enter a PIN, and there's no reason to make me confirm the transaction amount. Just process the payment and let me leave!