Answering for myself: It's another thing I have to remember, or visually look for. I have to remember the state of the keyboard, I have to remember even more key chords, or both. I have enough cognitive load going on keeping a programming, gaming, or design stack going in my head to add another load keeping track of the status of my input device.

Even should the actions become muscle memory (I own, but no longer use, a HHKB and know that muscle memory fits in), that muscle memory will fail me the moment I have to use another keyboard, causing a mental stutter as I consciously override my muscle memory (with the HHKB, that was escape and delete in particular).

Moreover, I can feel my way around a keyboard and find all of the keys I could need by the clustering and relative position to the home row. Since I don't rest my hands on the keyboard while typing, this movement is not at all uncomfortable or distracting.

That's why I like full keyboards, why even I could find a keyboard with more keys useful.

Yeah, I used to have a dumb terminal on my desk, and I used the macro functionality inherent to it to semi-automate all sorts of workflows for myself, it was very very helpful.