Ah, that makes perfect sense. One of those, “obvious once someone points it out” things!
So that question is off my list. I still wonder about someone using standard keyboard keys, but combining them with the layer approach. Not that I think it would be better than a TB, but even with the greater vertical reach compared to the TB, you’d still be reaching less than you would for a regular keyboard with 5 rows! Of course, you also wouldn’t have nearly the portability of a TB either! Still, I can see how it could still be superior to the typical keyboard today.
I could more easily see someone coming up with that approach to start and then later maybe someone would take that basic concept and further it with the TB variation. That’s one of the things that amazes me about this thing. It’s like having years of telephone development and then someone comes up with a an iphone - in 1950! You just jumped right over what I would have expected to be many years new ideas gradually being added!