Cash: Get out wallet, count out cash, get change that I'll probably lose anyway. I hate small denominations.
Card: Get out wallet, put card in machine, wait 10 seconds for authorization (I'm in Switzerland - their terminals take longer), sign receipt. I hate signing.
Apple Pay: See prompt on phone, which I'm already holding, with price and card info. Press thumb to button. Wait 1 second. Done. And I like thumb presses.
Not only does it save half the time on every purchase, but it obeys my arbitrarily finicky preferences on how I would like to pay. But you know what? Even if it seems like such a tiny detail, many people share those preferences, and the difference is more than enough to tip the scales of habit for those who do.