Erm, exactly the same does your average WW2 game? Modern combat games if you believe it or not are simply able to offer much more variation because you're not bound to something like you are in WW2.
Your average WW2 game doesn't differ from your average modern shooter, they used to be/mostly are based on the western front, around the time of operation Overlord. Which is equally as un-interesting.
RO however, wasn't an average WW2 game. The eastern front setting was completely refreshing when ROmod first came out.
Modern combat is far less dynamic because it comes down purely to who has the greater numbers, or who has the element of surprise.
Surely, advances in technology have led most major powers to have near equal quality of arms?
Think of an army US/China/Russia/Germany/UK etc, now think of it's main assault rifle, it's armour, or its combat strategy.
Simply put, there was a far greater variation of small arms, support weaponry, armoured vehicles, and combat strategies during WW2. Just because late 43-1945 has been portrayed to death doesn't mean that there is nothing left to do.
I'm not saying that game2 needs to be a WW2 game, it could be sci-fi for all I care. If you made a WW2 game, yeah, you are bound to the strategies and equipment of the time, but a modern combat game is less varied due to the perfection of strategies to minimise cost of life and maximise effectiveness during previous conflicts.