I have noticed that windmills are generally built in empty fields with no trees around, and I've been wondering why...

A windmill is generally way taller than trees and I can imagine that trees don't actually affect the flow (see picture).

But is this the reason why there is nothing around or is there something else that makes them waste so much space around? And would this be a realistic velocity profile?

If I search for the theory of external convection, the velocity profile looks like this for flow over a plateau:

In the second case, wouldn't the velocity be higher if there is an obstacle? Or is it because the obstacle is a porous medium that damps the flow? And lastly, is the velocity profile at earth level like that? Is there really an origin to it or is it fully turbulent and with different sources?