I've always been confused as to the success of the computer mouse. It doesn't seem like the ideal solution. Then again, neither do trackpads.
Without meaning to be argumentative, what would be ideal? In the absence of an actual better solution, one can explain the success of an obviously sub-optimal but existing solution by "worse is better" (https://en.wikipedia.org/wiki/Worse_is_better).
Touch screens are obviously very much modern devices, and, though they're far from ideal as the only input device, I can buy that, when used in conjunction with a keyboard, they are a good replacement for a mouse or trackpad; but don't they suck up power in a way that mice and trackpads don't?