Think of a way to monetize this mode to the extent that MUT is dominated by microtransactions and then Tiburon might begin to consider it.
That's the reason MUT is the exception - it quite literally is a revenue engine built into the game. A "sim play" DLC pack is something which will require a ton of programming / art support for addition of features and AI beyond what currently exists in the game and - unless you are thinking of something I am not - will only realistically see one transaction, that being the pay wall for the initial download. The economics aren't remotely similar and to that end it's not justifiable.