Looking at my local spots (in the different places I lived over the years) it breaks down to these DH bikes being popular:Yeah but this is further to my point - the Sunday was ridden by a fast and popular rider (perfect combo). Whereas you can get the same success pretty much with a slower, but more popular rider as you do with a very fast, less popular rider. Looking back at World Champs bikes over the past 20 years, there's plenty of examples of bikes that didn't sell very well, or were entirely unavailable to buy.
YT: cheap access to the sport, Gwin later was a bonus but they were abundant before
Giant, Specialized, Trek, Scott, KHS: LBS hooking up the kids that are into DH
Yeti: local dealer instrumental in getting folks on these bikes (had too many rails and was too heavy for me, so I had to miss out on an awesome deal)
Intense, Foes, Orange, Santa Cruz, Nicolai, Alutech, (Pivot): especially in the early years the only viable options if you didn't want a glorified XC bike; later more the enthusiast bikes for folks that know what they want; local dealer helps to increase numbers but often independent from support
Iron Horse: Sam Hill fanbois
GT: funnily in the RTS/LTS years many (Nico, King, Peat), lately not so popular although Wyn is quite a popular rider; might also have to do with LBS support