A “cap” feature isn’t as easy to implement as you’d think. What happens when you hit the cap? Does it start shutting down instances? If yes, which ones and in what order? And don’t say “I don’t care” because you do care—you are allowing your provider to basically cause an outage in your service.
If you do allow some kind of ordered shutdown of service, what is the UX going to look like? What is the API going to look like?
Having a cap is not an easy feature to design or implement. And on a backlog, it is going to be a “multi quarter, low impact” item—meaning it will never get built.