I guess it's functionality vs aesthetics. You could probably craft beautiful piano sounds out of a cheap plastic keyboard, but it has to look good on stage too.
I've played a show once where we shared some instruments with another band due to cramped stage. The keyboardist in the other band was playing a Nord Stage, which is a very expensive, but still plastic keyboard (they go for $4-5K).
Despite its iconic look already being a thing that people shell out extra $$$ for ("gotta have the red one!"), the performer put hers in a grand piano shell.
That is, a gutted grand piano (or a mock-up), with the Nord Stage on the keybed.
