Why do brunettes dye their hair blond but blondes never dye their hair brown?

that's not really the case i am a brunette but i dye my hair red and my best friend is a blonde who dyes her hair jet black..... it is not necessarily just brunettes who dye their hair blonde either.... some blondes go blonder some red heads get blonde streaks..... so all i am really trying to say is it really depends on the person... not necessarily their "group" (aka blonde, brunette, red heads, etc.)