It is interesting how the Army can only do one thing at a time. I joined when we were still training for Vietnam, though the war had been over for almost a decade. For the next fifteen years it was all conventional training. Institutionally, there are a couple of reasons for this, I think. First, doctrine is written by branches, and doctrine matters because it leads to money and manpower and material. Therefore, doctrine needs to be consistent and support the other institutional goals of the branch. Second, the schoolhouses have a limited amount of flexibility - this is generally a good thing, by the way - and a limited amount of time to teach. Again, this encourages a single approach to training our future warfighters. Thirdly, it takes twenty years to properly train a brigade commander. If we shift our emphasis on levels of warfare too often, they will be jacks of all trades and masters of none. I'm sure there are more reasons out there.

By the way, in touching on this thread's initial focus, I don't see how we can or why we should avoid promoting our best COIN operators to general. Success in war should be the first consideration for the promotion of generals (and shame on anybody who says otherwise), and counter-insurgency is the only contest in town right now. Does this mean some budding conventional Patton/Manstein/Slim out there will get passed over? Probably.