Overhead of HTTP/2 Stream Management.

I'm in the process of implementing HTTP/2 into Avuna, and I have a question.
>From a performance point of view, why do streams maintain a open/close
state? There seems to be a considerable overhead for it, yet it doesn't
seem necessary. Think of packet IDs in DNS, it just returns with the same
ID to say it is a response to a specific request. What is the benefit of a
detailed stream-like system, versus a simple request/response identifier?