It is not all that rare to have a great question or research project that is very interesting on its own and has wonderful applications.
No matter how genuinely you think you have a problem worth looking into for solid objective reasons, you should acknowledge that others may not feel the same.
This doesn't mean that the problem is irrelevant, this just means that you haven't found a fellow mathematician with suitable interests.
There is no guarantee that such a fellow exists on MathOverflow.

It seems that your question has been unable to find "a relevant mathematician", but judging by the amount of upvotes and comments, it hasn't gone unnoticed.
It might be that some very relevant mathematicians have looked into your question and decided it is beyond their reach (and that it is beyond their resources to start actual research on it).
It might also be that there simply is no relevant mathematician on MO, or, in the worst case, anywhere on the planet.
Good or important questions don't always get the answer they deserve, and improving and motivating the question might not change that.

You will just have to accept that the MathOverflow community cannot deliver an answer to all problems, no matter how tractable or important you think it is.
It is ok to ask for advice at meta, but complaints along the lines of "My question is very important and interesting. Why don't you guys agree and solve it?" are not very useful.
(This is an exaggeration of the tone you used, but I believe it is this flavour that has earned you downvotes at meta.)

What can you do, then?
Two things come to mind:
First, try bringing your question up with mathematicians outside MO that you know to have relevant interests or skills.
Second, try looking for simpler problems that you still can't solve or any kind of toy model of your question; if you can't solve them yourself, you can ask about them here or at MSE.
Simple and short related questions help you in several ways: not only are they helpful steps towards understanding and solving a big problem, but they are also more likely to be read and answered by other people in the internet.

I can't comment on the importance or other aspects of your mathematical question.
I'm yet another one of those mathematicians that are interested in something different and lack the knowledge to give a simple but very useful answer.

You are not alone with your situation:
I don't ask many of the most interesting and important questions that arise in my research at MO.
I know that to get a useful answer I'm usually much better off sending an email to a well-chosen colleague in my narrow field which is not well represented at MO.
MO can't give everything I want, but I appreciate it for what it can give.