In iTunes you drag and drop within the interface, you don't have to rummage through folders on your hard drive to find the music you want. iTunes provides searching and advanced sorting functions that you just don't get browsing through files and folders.
Besides, how does your music come to be organised in the first place? If you are organising your music into folders arranged by artist and album name by hand, that in itself is far too complex for most users.
iTunes provides a great end-to-end music management solution that is easy enough for the most inexperienced, and extensible enough for the most experienced of users.
Sure you can organise your music collection by hand and manually drag and drop folders, but why would you do that when using something such as iTunes is so much easier?