I think it’s a combination of things. My experience definitely parallels yours: when developers have access to the bill they tend to realize the cost of the services they are using. Sometimes even resulting in optimizations to those costs.

At the same time AWS can get fucked with how horrible their bills are to understand. They don’t exactly go out of their way or even slightly on a good path to deliver a clear bill.

So even if the developers have access to the bills they might just end up with an impenetrable list of bullshit from AWS