

We figured it out in the last millennium, I think we can figure it out again.
The real reason would probably be that you’d need to make the soles out of rubber again instead of the cheap foam that almost all modern (fast fashion disposable) shoes are made with these days.
They work great until they don’t. I’ve had the same experience, be prepared to replace it occasionally because it’s usually near impossible to disassemble and clean the pump mechanism completely.