And the thing is they DID actually do it - for BECMI, in the Companion set. Where they had Dominion management rules and the War Machine for that kind of mid-high level activity. They just never did it for AD&D IIRC - which I've always found kind of odd.With respect, in AD&D they gave you some followers, and told you jack about how to play kingdom building.
"They knew what to do with it, but didn't actually do it," seems an odd assertion.
(Now it's been decades since I've looked at those rules and even longer since I actually used them in a campaign, so the rosy memories of my youth that say they worked ok are probably wrong - or at least missing all of the parts we ignored to get them to work. But they did have them! They tried to fulfill that promise somewhere!)