I'm pretty sure the big difference is that Apple built on top of credit card infrastructure and Alipay (from what it sounds like) is its own payment system. I'm guessing that's a larger regulatory hurdle in the US and many companies wish they could.

The sluggish performance and fickleness is 100% on the terminal. You can see an analog in how physical credit cards work on different terminals. Some you must insert your credit card only at the designated time. Too early and the cashier needs to tap a few buttons to reset the process. You must not remove the card prematurely. Other terminals you can insert your card whenever and it scans it pretty quick--usually before they're done ringing up items. Similarly, some terminals prompt early for ApplePay, aren't specific about which part you wave your hand over, and are almost instantaneous in completing. Others are the exact opposite.