Instead of bashing Apple, use some simple logic. iTunes, iCloud are repeating purchases and Apple Pay is primarily a single transaction every time. Every time I buy a song on iTunes, my card is dinged without the hassle of completing a single transaction.
Second reason is ApplePay is intended to make purchases transparent and keep your identity from the vendor. Apple already has your credit card info and knows who you are. And I am sure there are financial reasons in the way AP transactions are handled and fees involved.