Frankly, I'm a fair bit surprised too. I don’t think this number of downvotes is justified, but I would try to list possible weak parts from my point of view:
As I commented (more on that below), in my opinion there is a closely related question Why are HCl fumes white? I’m unable to single-handedly decide whether it’s a duplicate or not, especially given how sparse the origin is in terms of elaboration and how exhaustive yours is. If anything, it probably would make sense to keep the newer version of yours, shall it be concluded a dupe. Maybe others had more confidence that this is indeed a duplicate.
A list of three questions and five others later (eight in total) could be interpreted as a sign of a lesser focused question. I’m not sure bringing up a complex example with $\ce{BF3}$ was a particularly good idea since scattering explains the phenomenon in general terms regardless of the nature of the substance, or at least connecting both indirectly.
Somewhat overly-complicated suggested explanation when a simple
$$\ce{NH3(g) + HCl(g) -> NH4Cl(s)}$$
would already clarify a lot for yourself and the reader, and is arguably easily discoverable.
Some users cannot stand YouTube's “educational” videos. Granted, there is a handful of great channels, some of which are listed in our suggested resources for learning chemistry, but the vast majority of online videos are just badly executed clickbaits created for collecting ad revenue and are a waste of time and brain cells. Due to the dominance of the latter cohort by the sheer numbers, some associate YouTube links with subpar content.
P.S. Let me assure your question is far from being “heavily down-voted”. I have a question on another SE site with ten times more downvotes (over −30) and I don't think this made me worse kind of a human.
I'll take this opportunity to also address your comment:
@andselisk when a moderator promptly puts a link under a question without words, it might be interpreted as "this is easy and could have been looked up" and result in several down votes. Was at least the first part your intention (i.e. "this was easy and could have been looked up" or was it just meant to help others to formulate an answer. I'm scratching my head trying to understand why there votes are currently -4/+1 and just grasping at straws for an understanding as there are no explanations provided for them so far.
A barebone link to a neutral website like Wikipedia or SE can be interpreted as anything, really: a quick help, duplicate proposal, suggestion to edit. These are just URLs and don't carry any negative or positive feedback.
You've probably noticed that these days I mostly do edits and “porcelain” — as ProGit authors, I don't like the term “plumbing” routinely used to describe mods' cleaning activities. I don't have this much time at this moment to roll out well-written posts, let alone think how one's feelings may be affected by a Wikipedia link.
There is a theory for Q&A sites claiming that the quicker the response to the question is, the greater the chance the user is going to use the site again. It doesn't matter what kind of response, it's just the most people can't stand being ignored for long and want a feedback as quickly as possible. I personally value your input and I honestly think it would be a shame to loose such a thoughtful and curious user, even temporarily. I'm sorry that this time my input didn't work as intended.
As for
I'm scratching my head trying to understand why there votes are currently -4/+1
the only sure thing I can say for sure is that +1 here is from me because you put tremendous amount of effort and it's hard not to respect that.