The OS would need an interaction overhaul to make it work with touch - the hit targets are all the wrong size and a lot of behaviour relies on hovering over something. Couple that with the fact that the screen is at the wrong angle (I find it makes my arm ache just using an iPad with a keyboard and having to reach over to touch the screen) and I think Apple aren't too far wrong.
However, as someone who likes drawing, the way the Surface Studio folds down to an angle that is better for touch and pen does look pretty good to me.
I think it's more that retrofitting touch to a desktop OS - any desktop OS - is painful. Microsoft started it with Windows 8 and it's nearly - but not completely - done years later with Windows 10.
I suspect Apple has probably started retrofitting OS X privately, but released the touch bar as an interim solution.
The touchbar as a design decision makes a lot more sense when the brief is "Add touch to the Macbook Pro line... but under no circumstances step on the toes of the iPad Pro"