How come wallet is not able to scan my gift cards?

Reward cards but not gift cards > Use Wallet on your iPhone or iPod touch - Apple Support

Apple Wallet can store rewards cards (also known as loyalty cards), credit cards, debate cards, movie tickets, flighht passes, and coupons. At this time, there is no option for storing gift cards. For more information about the Apple Wallet, please visit Use Wallet on your iPhone or iPod touch - Apple Support