Why can’t I use Apple Pay or my Wallet with my IPad Pro in stores?

iPads do not contain the Near Field Communication technology that iPhones and Apple Watches do that allow you to use Apple Pay in stores. You can still use Apple Pay in apps and using safari on your iPad Pro.

You can let Apple know your thoughts here:

Product Feedback - Apple

Personally, I can't imagine that people behind me in line would be very happy if they had to wait for me to pull out my iPad to pay for something.