Part of this is the fear that some officers, thought to be very promising, will crash and burn if confronted with a determined opponent in a simulated battle. This has happened, and the military custom is to avoid this sort of thing. Save failure for actual combat. This is a hard habit to lose. Typically there are a lot of people killed in the first battles of a war, because commanders had little experience running an actual battle. But there has been growing pressure to change. Partly it’s a generational thing. Since the 1970s, there have been more and more commercial wargames on contemporary situations, and these have been very popular with junior officers (and a lot of the troops), but less so with the senior folks. Moreover, not all junior officers cared for wargaming out battles they might actually encounter in the future. The manual (and difficult to use) wargames of the 1970s have given way to computerized ones, which are much easier to use, and more officers use them. The military, as an institution, is under pressure to let commanders officially use wargames competitively, with another officer commanding the enemy forces, with both of them under orders to win at any cost.
Another problem area is the search for a wargame that will combine those used by the army, navy, and air force. The army and marines often use the same sims, at least while dealing with ground combat. But the navy and air force operate in a different environment, and when they have to account for what the army is up to, often use sims that have a different take on land warfare. This causes problems when all the services have to operate together, and efforts to resolve these differences continue.