I just think the simple answer is that there is not a large enough market for a game designer to risk the development costs.
If a Sim is somewhat realistic in the depiction of warfighting, there will be long periods of nothing happening. As a general rule, games where nothing happens tend to be considered unfun by a majority of the game playing market.
I love sub sim games, but to be honest SH4 has its dull parts. Going from Pearl to the Japanese theater even at 4K take a while and there is a good chance you will pop out of TC just after being sunk by an island, ship, or plane. When I play SH4, I usually have a movie playing on my other computer just to pass the time.
I imagine that more and more of the gaming community wants games they can play on their tablet/phone in between checking their status on face-space.
While there will always be a small group of weirdos like us who like Sims, I think the number of non-sim gamers is growing as their attention span shortens.