Beside agreeing with the "all of the above", I personally, I think it's a "flavor of the month", or a "cool factor" thing. Knives just tend to go that route..... it's always a big circle when it comes to knife type popularity......... I've never been able to discern the rhyme or reasons of why a particular type of knife is popular, and another is not, and how that can change so rapidly.....but it does.
I've made a number of my EBK series knives as "Neck Knives", and they have always sold well in that configuration..... which for me is nothing more then deleting a belt clip, and adding paracord or a bead chain through one or more eyelets. What I have noticed is that the, for a lack of a better term, more educated/seasoned custom knife buyer, will generally buck the current trend(s), and buy what they like, even if it's not popular at the moment, but for knifemakers who sell their knives, one person's money is as green as the next's.
I also did research and made them (my EBKs) under the legal blade length limits for all states.....well, except for a few cities who have fluctuated over the years on the blade lengths that are legal. At the time, 2 3/4" was legal in all STATES, but it was/is impossible for me to find all the legalities of every U.S. city.....so I always have a disclaimer in the paperwork that it's up the buyer/owner to follow all state and local ordnances/laws.