Why do they still have the 3 standard hardware buttons?

I just don't get it. Maybe someone can explain me a good reason for it, but why are all the new phones (bigger than 4.5" screens) still having the 3 standard hardware/capacitive menu buttons in front? Doesn't Android 4.4 allow translucent software keys like on Nexus 5? It even allows more space for a bigger screen in the same size of the phone.

Edit: Sorry for the confusion, but I did not mean 'menu' button in particular but the 3 standard buttons (back/multitasking/home/menu).