you can do exactly what you're talking about, you just didnt bother to look it up. it is done the way it is because it is intuitive to organize things that way and it is a good way to make the actual organization of data on a storage device human readable. most people have no use for organizing things the way you are talking about 90% of the time, bit because usecases do exist where it is helpful it has always been possible to do that on linux. depending on the apps you use it may not be exposed graphically, but it can be done.