My take on this is that bitcoin, and crypto in general, doesn't suit their way of doing business. After all, what extra business would they acquire, and what hassle would it bring them ? Amazon has its own "money": amazon gift cards. *these* you can buy with bitcoin if you want to.
The whole model of Amazon's business is to have a very secure financial treatment, with the full legal machinery behind it. You are almost never scammed by amazon. This is why the credit card model with the possibility of reversible payments and legal framing is extremely important for them. Anarchist obscure irreversible payment methods have not really a place in their business plan. They are the opposite of dark markets, for which crypto is the ideal payment method.
You are correct up to the point that it makes financial sense to use them. If enough customers use bitcoin, Amazon will take it.