Because a nice, big bun + 3000 bonus points to an outfit! (And you need LONG, THICK hair to achieve a nice big bun!!)
Case(s) in point:
... ok maybe not the last one. But you get the POINT :)
(image sources: facehunter/facehunter/studdedhearts/buystarwarscostume)
Do-It-Yourself with these amazing videos!
(It's ok to not understand Japanese.. this video is pretty much self- explanatory)