Unfortunately, most folks out there who are only interested in firearms for self-defense tend to just follow the example of the Military or Law Enforcement, and now that the FBI has transitioned away from .40 S&W to 9mm Luger, folks are following suit.
It also doesn't help that there are a lot of extremely vocal 9mm Fanboys (including writers/editors for various publications) who like to pretend that it's the ultimate, one-size-fits-all self-defense cartridge and thus make all sorts of ridiculous statements like that modern 9mm Luger +P ammo is roughly equal to .40 S&W, ergo folks who are just looking for a good self-defense cartridge get fooled into thinking that they'd be better off selling their .40cal pistol for a 9mm pistol which is just as powerful, but lighter in weight with less recoil which is much cheaper to buy ammo for.
Eventually the FBI will decide that the 9mm isn't effective enough and that it's more important for agents to be able to put a threat down as quickly as possible than it is to cater towards the recoil sensitivity of certain agents, at which point they'll either switch back to .40, switch to another cartridge, or contract someone to design yet another new cartridge which better suits their needs, then everyone will want whatever they're carrying.
I honestly wish that one of these days that a bunch of different websites would collaborate on an elaborate prank/experiment in which several publications run a story in which the Military/FBI have adopted a revision of the Gyrojet as their new Standard Issue sidearm/cartridge, meanwhile fake listings for said cartridge/firearm would be all over major online firearms retailers like Bud's Gun Shop, just to see how many folks would place orders for them.
I have a hunch that there would be a whole lot of folks who would immediately flock to said retailers, regardless of how ridiculous/impractical the supposed choice of the Military/FBI may be.