I think that it comes down to friction. When you go for a coffee you will give cash or you will use card. When you use card it can be one of quite easy options:

I think that it comes down to friction. When you go for a coffee you will give cash or you will use card. When you use card it can be one of quite easy options: signature, PIN or just contactless payment. I was easier inclined to buy something on Play Store when it was just added to my phone bill. Only because I had to just write the password that I already know and use. Now if your service requires registration and one more password, it must be really worth it. Card payment is a bit of a hassle - imagine going to an odd store somewhere and going with the same procedure at the cash register. Write down your name, card number, valid-to date and CVV. Also a password and a billing address. For me it is a hassle. I can't imagine how awful it must be for most users. It still comes down to easy micropayments. Where one account will take you everywhere.