Limited by evolution
Humans evolved to make large motions with limbs; moving from one place to another, lifting things etc. and manipulate small things with small precision movements of the hands.
For the vast proportion of the population with no handicaps it is most efficient to use the small precision movements that hands are capable of. In our high data rate environment hands are the only thing that is going to cut it, and until a device is capable of operating with minimal force and displacement, whilst maintaining accuracy / minimising false readings it is not going to succeed.
We are constrained by our anatomy and I cant see the mouse and keyboard begin replaced until we have reliable brain interface translators to bypass our collection of bones and muscles.