I'm not sure it's necessarily a case of that they won't fix it, it's just a case of priority. Like all development projects, they'll have a backlog of issues and features that they want to address, and how they go about prioritising them is up to them.
I'm not sure of the original decision behind the 302 redirect, and I can't think of a good reason why it should work like how it does. My honest guess would be that it was just built as a straight-forward redirect as a simple development approach, rather than a conscious decision to not account for correct status values. That is pure speculation on my part though. Though I'm supplying this as answer, someone maybe able to offer more insight here, if there is any to be had.
The best thing to do would be to make sure they're aware of it as something you'd like to see changed. Raise it on the UserVoice and also considering reaching out to support.
why Sitecore doesn't fix this
- Only Sitecore knows. I can only assume that since this has been in Sitecore for a very long time, at the time it was not considered a SEO faux pas. – jammykam♦ Oct 18 '16 at 22:10