There's certainly wastage in large organisations. Over provisioning or keeping that huge S3 bucket full of data from some long forgotten project.

I suspect a lot of the huge AWS customers just eat this because it's so hard to mitigate.

If a business has hundreds of AWS accounts it becomes very hard to track, and if each account can only shave a few hundred dollars a month off their individual bill then there's very little impetus to actually do the work for the individual teams. Despite that possibly adding up substantial savings for the overall business.