Think about motivations for a moment.

The seller is motivated to make the buying process as easy, fast, and uncomplicated as possible. This is a direct correlation with how many things they sell, and in response how much money they make.

On the other hand - consumer opinion and regulation forces them to ensure that the buying process is secure, that someone else isn't buying things on your account, that they have proper logging of what goes on, etc.

The seller shouldn't "Fix" the buying experience by removing the security aspects of it. They should fix the buying experience by using modern authentication like passkeys and ensuring that their applications and sites support password managers.