Why devices with monochrome display have disappeared completely?

I'm looking for a GSM phone for my grandmother. She use to complain to every colour screen phone about not enough contrast, no ability to enlarge text, too small pixels and too stupid graphic work when something significant may be indicated by changing from blue to white which is too easy to be unnoticed when your eyes are enough weak.

Why there are a lot of ugly granny-phones with absurdly giant buttons but tiny display and no high-contrast mode with respect to those who sees badly? Monochrome displays are really good for those who at least can see individual pixels of the monochrome display, so it is unexpected for me to see them extincted even from cars.