Exactly. Google does not have my credit card and I don't want to give it to them. Amazon already has it. Just like I prefer to use PayPal when I can to avoid giving a new online merchant my credit card directly, I could now use Amazon for that purpose.

If I hadn't ever created a PayPal account in the first place then I would have no motivation to make one. With Amazon I already give them the credit card info to make purchases on Amazon. PayPal is just a middle-man so I have no reason to use them already.

Well, except that PayPal lets you receive payments too. Now that I think about it, I believe I created my PayPal account originally to accept payment for a website job. Only later did I add my credit card to make eBay purchases. So I can't completely replace my PayPal account with Amazon services yet.