Why do planes employ vortex generators if the laminar flows exhibit a far lower skin friction drag than turbulent flows?
Laminar flows detach from the surface earlier than turbulent flow does, which means that with everything else constant, a laminar wing stalls at a lower angle of attack, and does so more suddenly and with less warning.

The unsteady nature of a turbulent boundary layer allows it to extract more energy from the freestream (flow which is not slowed down by the wing), thus the boundary layer stays energized and slows down later. This, as you have mentioned, increases drag, so there is a tradeoff between delaying stall and increasing drag.

You'll find VGs on the wings of trainer aircraft,so that they have forgiving stall characteristics...

...STOL/bush aircraft, for lower stall speeds...

and near control surfaces of all kinds of aircraft, to retain control when the control surface itself is in high angle of attack. This also increases their effectiveness so the designers can get away with making them smaller.