Well .. here is the reason.
While I'm sure you could do it, and keep it small, you would have a problem with ...
(our favorite killer ...)
Noise!
Imagine the hovering vectored thrust vehicle near the scene of an accident, etc. I'm sure that no matter what the configuration, that the thrusted vehicle will be much louder than the conventional rotorcraft ...
I'll allow for being wrong, possibly someone could come up with something to muffle it, but so far all designs are large, and noisy.
Figure out noise first, and the other issues brought up above (power, fuel usage) and it would sell quickly IMO.