Kewl some responses. Please excuse any bouncing around I do in my replies. Also I've had several discussions on the use of dart throwers here in these forums before if you want to glance at those.
Firstly for those wondering why these don't end up becoming the gorean equivalent of an arquebus or even a colt revolver it's simple. They are manufactured by kurii from the steel worlds for specific operations, usually in remote areas. The ammo, as far as I can figure, is a self contained quarrel that uses some manner of compressed gas. Basically a crossbow bolt with an explosive head that operates more like a CO2 paintball gun than a conventional rifle. So ammunition is entirely dependent on the steel worlds, and their isolated outposts. Considering all the factors these weapons would not be easily reproduced by 'normal' goreans.
A gorean builder or scribe might be able to manufacture some of the fittings and the overall shape of the weapon, but the ammunition is likely beyond their ability to reproduce. Especially once cultural affectations are thrown into the mix. Plus kurii & other agents that found out about such projects would in all likelihood have the individual killed.
To my knowledge the kurii in the books never used them, instead relieing on close combat, or the occasional smuggled energy weapon. However, since a plasma cannon obviously would raise to many eyebrows no matter the user, many other producers began producing their own take on gas propelled quarrel weapons. Since they're canonish, and have fewer animation issues compared to bows they seem to have become the standard kurii ranged weapon. Basically, it's all they have to shoot back with.
In other words, unless you want rayguns, these are a nice middle of the road option for meter pew pew.
Now for possibly the biggest issue that Darve brought up. From my own experience using my dart thrower, over the last four years there will be a percentage of ignorant sorts who scream "OMG riflez111". However, the majority of these are more often than not looking for an excuse to claim invalid, or to try and come off as 'legitimate' role players despite their heavy metal costumes. In other words, they'll whine anyways.
I cover this subject a bit more thoroughly in the notecard I include with my dart launcher so people know this is a toy you only use in rare circumstances, and it really shouldr never be found openly in places like cities. Since you're unlikely to see a kurii in such a place, then the potential issue is lessened.
Now, I do have some ideas for a kurii sized bow now that I'm getting more familiar with the way the prim avatar works. Seeing as I've been selling a bow that'd fit a kurii for years it's a supposedly simple idea. But, as others discovered before me, fitting a weapon to the prim avatar is often a pain. Some of the kurii weapons I looked at don't even have animations for them simply because of the difficulties in compensating for the nature of the avatar.
So again, these dart weapons are the easiest solution, and seem to appeal to those who want to remind folks of gor's sci-fi stylings. Since running into a kurii is already an unusual event, the weapon they use seems a minor issue in comparison.
I am an opionated artist, not a typist or english professor. So, excuse my typos and the occasional mispelling. Also yes, sometimes I will say weird things you need to google to figure out.