The problem is that Poser doesn't require such files to be placed at a specific place. The result is vendors placing them everywhere, inside and outside the library, so we have no control or standards for how to handle this. It's pretty much a mess. Some vendors do put them in a separate folder, but the folder itself is still inside the library (doh!).
Poser doesn't require _any_ files to be placed _anywhere_. You _could_ put your textures and OBJ files in random folders. It's a bad practice, so people don't. Just like they also don't just put them loose in Textures, or even in Textures > Figure (unless they made the figure).
People aren't doing a consistent thing because the standard hasn't emerged yet. I used to have a bunch of "MAT" files that were camera files, before poses became the standard way to set material presets. And it was _years_ after the introduction of material collection presets before anyone besides a few techies used them as well as MAT poses, let alone instead of. Heck, I remember when OBJ files were often in Runtime or in Library. Poser World's old content put textures and OBJ files all over. Saying that right now, when we're only about two versions of Poser into people actually trusting PMDs to work, the community doesn't yet use a Morphs folder just like they do the Textures and Geometries folders doesn't detract from the fact that the obvious best practice is to be consistent with externally linked files, and put PMD files in a Morphs folder with internal structures and practices similar to the Geometries folder.
If Poser content survives, I won't be surprised if brokerages come to enforce a structure and naming convention for morphs as they do textures and meshes, and if that structure is consistent with the conventions they already have for textures and meshes.
This is why I keep mine together with the INJ/REM files, after manually removing the path info from the PMD. The down side of this is that it makes it impossible for other vendors to reference my PMDs if they want to make expansions, but that has never happened anyway, so I don't make it a priority. That's the only reason I can think of to justify creating external folders.
Or it's never happened because your morphs are in the wrong place. I know I've deliberately not only given up on using the morphs I own because of this practice, I've not even glanced at anyone else's for that exact reason. Why bother when I can't build off them? Especially when they're utility morphs like yours?
To be clear, I've done this in general, without any knowledge of the specifics of your products. I've just been burned so many times by other people's morphs I found useful but couldn't build off of that I've given up.
Also, the other benefit is namespaces. I don't have to worry about someone (including myself) accidentally overwriting my PMD files or bogging them down with complex names that are hard to scan. Everything is consistent, so everything is easy for me and my customers to find and/or avoid. Again, for the same reason the standards for textures and meshes exist now- and are equally unenforced by Poser itself, it's best practices to simply extend that standard to PMDs rather than come up with something new, inconsistent, and unable to work with the rest of the community.
You _can_ go out of your way to do something different that excludes everyone else from working with you, clutters up user's libraries with unfamiliar files, and makes it a bit harder for them to restructure their library (PMDs with similar names, needing to move the PMDs at all but not necessarily knowing about them, etc.), but why? There's zero benefit and lots of drawbacks.
Oh, and we will have to get a standard, or there will be no new successful Poser figures. Any successful Poser figure will have to have characters that are pure dial spins, and you can't do dial-spin characters without being able to count on injection working for you.
