War in the modern world is not fought with huge pitched battles like the average RTS.
It is fought in small skirmishes between a squad or three, large invasions that take over a town in an hour or less, or planes with rather large bombs wiping out entire military bases.
Trench warfare no longer exists, and that was the main thing about RTS with guns.
Most of the listed RTS are either not set in the present day or in WW2/future. The others are inaccurate representations of modern war.
Red Alert is science-fiction - not an example of modern day warfare.
If you made an RTS that was a true representation of modern war, there would have to be a MASSIVE amount of ducking and hiding or fights would be over in ten seconds. Then a plane comes along and bombs the area to hell anyway.