People might put them in M4 Morphing Clothes since that is a folder that DAZ started and people don't want to add another folder when one already exists. I always put all M4 clothes into that folder anyway so I can find it easier. Same for the V4 Clothes. Putting it into a common area makes things more able to be found so that is why some people might follow that. I might not remember that the dress is called Alice Dress but if it is in the Clothes folder I might be able to find it.

You can have folders inside of folders so the M4 Morphing Clothes can contain every outfit you have for M4 and it is a common source. Or you could have M4 Clothes, M4 Fantasy Clothes, M4 Sci-Fi Clothes, M4 Modern Clothes and put all the things in the individual folders.