From personal experience, just boredom. Lol Having the same hair color for years you want to see a change to shake things up, at least just to see how it looks. The style suits alot of woman, not to mention, hair does grow back.
Because males usually perfer blondes
They want to stand out like a "Glo-worm"....look at "Me". "Attention"!
Some of them would rather be blonde.....some people look best blonde.