> Why would any serious musician spend 22k Euros on this piano... inferior instrument in volume, tone, tone control, sustain, and pretty much all the features

It's a different sound. For a certain type of music, it's superior to regular pianos.

There are how many kinds of electric guitars, acoustic guitars, woodwinds, brass, strings, percussion instruments, electronic gear...? Very very many. Even in piano-land, different makers have characteristic tones. A musician hears a sound in their head, and wants to replicate and shape it exactly.