The trick to the hobby shops is you gotta train 'em! You gotta take your junk in there and show 'em what you got. Then you'll kinda see the lightbulb turn on. I had the exact same experience at the one good hobby shop in town here. They all looked at me weird at first. But I just kept coming in and buggin' 'em. And I showed my stuff to them. Now they carry Axial beadlocks and all sorts of driveshaft parts, they have the Axial crawler on order, etc.
I think the killer is that many hobby shops have to go through specific distributors (or something like that) so stocking things like RC4WD beadlocks or aftermarket chassis and other things that aren't distributed through "normal channels" can be difficult.
We also have like a hobby shop like Big Mike described. D&D nerds that know jack diddley about anything. Those types are just straight-up un-trainable.
WOW you got it pegged..... Because hobby shops see YOUR stuff they just go and order willy nilly. The thing with a successful hobby shop is you have to be flexible!!! I cant go order all the Kanai stuff from Kyosho cause in 3 months there will be a new revision and most times the distributors will not take it back. I cant justify carrying 10 axle cases for the tlt's, I have owned 2 or 3 tlts in the past and I still dont stock them cause most of the crawler guys order it online anyway. You can not afford to be a niche market but you cant carry everything, If every 3rd customer came in looking for crawler stuff we would carry A LOT but its every 30 or 40th customer that asks and you just cant do it.