Any answer we can give here will be purely speculative until the miserable miscreants reveal their own rationales.
In skimming the query, I can really only conclude that the issue might be one of your style of presentation. As originally written, it was as has been said, a wall of text.
- Walls of text are unpopular because we have to slog through them. This demonstrates that you don't know how to present your ideas.
- Your writing style is also slightly jocular and slightly careless: too many uses of words like "dealio" and "thingy". It demonstrates that you don't care enough to learn what the "dealio" is actually called, with the result that a respondent might not care enough to bother answering.
- Your query is about twelve times as long as it needs to be. It basically boils down to Would a set of guns mounted 180deg apart on a rotating platform as per the design sketch be a viable design for any type of weapon (handheld, emplacement, or vehicle mounted)?
- Per T. Sar's comment, some users immediately downvote something that is made to entertain a silly idea instead of actual stuff that can be used in creating a piece of fiction. The "Just a random idea I had" might be enough to trigger this instinct.
It's not that long questions are inherently bad. It's not that jocular wording is bad. It's not even that long-winded presentation is (necessarily) bad. It's just that, in my opinion, the perfect storm of all these things, and possibly others, ticked a couple readers off enough to downvote your query.
That said, stylistic issues aside (which I think you could profitably edit away), I honestly don't find your query to be either useless, unclear, or particularly lacking in research. (Those are what we consider especially valid reasons for downvoting.) Thus, I wouldn't downvote. Though I wouldn't necessarily upvote either! And that's a different matter.