I know why people did it, I started out with Poser 4 and Poser Pro Pack which didn't have a material library, what I don't know is why people still do it. It's not like materials now days would be compatible with Poser 4 anyway. 

Also, I hate prefixes in folder names like "!!!! MAT FOOBAR" or whatever other character, it adds one more step to a product install process, renaming the folders...