AFAIK this is pretty spot on. I don't know if it's "policy" or what, but based on talking with AWS account managers, AWS does not often (or ever) create custom AWS services/products for individual customers. They do however let customers submit feature requests, and then let customers lean heavily on AWS to implement those feature requests in the public AWS services.

I think this is what leads to a lot of MVP-type services. A large customer clamors for some individual niche feature, AWS implements a MVP version of it, and then the team moves on to the next feature request (which might be for a completely different service, leaving the MVP in a perpetual MVP state).