Most of the actions just duplicated existing UI elements.
So when you go to the deck to perform an action, you mentally context switch away from the keyboard, so your brain is looking for different clues.
So even with a touch bar + function keys, the function keys stay in keyboard context, but the touch bar requires that switch in any case. Maybe taking your eyes to the touch bar is enough of a context switch, mentally.
The problem was that it was too much of a tradeoff. Either a touch bar or function keys. I need function keys. The touch bar was useless for this purpose (no tactile feel).
Apple could easily have done both. There's more than enough space even on the 13" macbooks. It would have taken a bit of space from the vertical range of the touchpad but it's already comically large anyway.