Because it’s expensive, bulky, and unnecessary. Something like this already exists: the Optimus Maximus keyboard. And while it’s a cool concept, it’s not without its rough edges. [1]
Wasn't the Maximus made with tech that is now 10 years old? I can imagine that costs have decreased by at least an order of magnitude by now, now that oled is much more mainstream.
I wanted one of these when I first spotted it, but in hindsight it would be too dependent on software to work and I'd probably end up spending ages setting it up when the right thing to do would be to get blank key caps.
