The large enterprise vendors are not prise-sensitive. They're on AWS because you never get fired for picking AWS, and there isn't really any other choice for these vendors regardless of AWS ripping you off.

At this point S3 is a standard interface. All sorts of cloud providers and open-source projects provide S3. If you're on AWS, price isn't the reason. You pick AWS because you don't see your company taking a risk with anything else.

S3 doesn't mean expensive. AWS does. But AWS users are fully locked-in, they'll pay whatever the price is.