The size of the spacebar on a standard keyboard takes up the space of 6 keys; but people will push the spacebar in the same place. It's nicer for the thumb to be able to access more keys, and nicer to not need to rely on the pinky finger for so many keys.
I think most keyboards which give the thumb more keys also follow this trend of taking away the numpad, F-keys, arrows; often even the number-row as well. (Maybe just my bias, but I think most keyboards with more thumbkeys are symmetrical, too).
While there's a trade-off "moving hand to a greater number of keys" against "complexity, like layering".. I think the small keyboards make more efficient use of the hands compared to standard keyboards. -- My guess is that people who try designs with more thumb keys then think layering is pretty neat.
Yes. Classical keyboards are inefficient in so many ways.
Consider that thumb is responsible for 50% of hand function [1]. And we use it to press only one button - the space bar. While pinky is the weakest finger andd we use it for the greatest number of keys...
Not sure about other people's experiences, but to me the thumb isn't that useful as a typing digit because it can't arch. Multi-row thumb clusters are useless to me because I can't press the upper rows with my thumb without pressing the lower row as well.
To me, a "thumb cluster" should be just a single row of 1.5u keys. Any secondary rows above those aren't reachable by thumb, so they rarely get used, and therefore might as well be removed.
Maybe others have a different experience, but I still use my thumb mainly to press the space bar and enter keys. All other thumb keys are modifiers and layer switches.
I think most keyboards which give the thumb more keys also follow this trend of taking away the numpad, F-keys, arrows; often even the number-row as well. (Maybe just my bias, but I think most keyboards with more thumbkeys are symmetrical, too).
While there's a trade-off "moving hand to a greater number of keys" against "complexity, like layering".. I think the small keyboards make more efficient use of the hands compared to standard keyboards. -- My guess is that people who try designs with more thumb keys then think layering is pretty neat.