This question is a follow up to my broader question, What's the point of blowguns?, in which I asked about their overall purpose in the game and how they compare to other weapons. Generally speaking, the comments (some of which have since been deleted) and answers explained overall how the weapon isn't an "optimal choice" and explained reasons why it might exist, but the answers did not cover what I eventually realised was the thing that didn't make sense to me the most:
Why did the designers list this weapon as a martial weapon?
It's just a small tube that you blow on one end and needles fly out the other end. It's not comparable to, say, a longbow, or even a net, in terms of skill or complexity. Not to say that it's super easy; I'm sure it's harder than it looks IRL to actually hit your target with one of those things at its maximum range. But if a shortbow — another weapon that's harder to use than it looks — is listed as a simple weapon, why is a blowgun listed as a martial weapon?
My perspective on this has led me to conclude that it must have been a mistake; as the DM during a certain game in the past (when I asked my original question) a certain PC wanted one but was only proficient in simple weapons, so I just ruled that they had Blowgun Proficiency as a free proficiency to "fix" this mistake. Such as thing should surely be listed as a simple weapon, but it's not been mentioned in any errata so this implies that the designers do genuinely consider it a martial weapon.
Since it's not explained in the PHB or anywhere else, I imagine that only the designers would be able to shed some insight on this matter, hence I'm looking exclusively for the reasons the designers have stated — if any — to explain this design choice (and I've included the designer-reasons tag).
What it is about the blowgun that makes it on par with weapons like longbows or nets (or any other ranged martial weapon) rather than shortbows or darts?