But the thing is, WotC doesn't need to do this for people... because with DMs Guild any person out there could write up an entire system themselves and offer it on DMsG for those that want it.
But the fact that no one bothers to even try might be an indication that it actually isn't all that wanted or desired of a system in the first place. Which of course would then tell WotC they definitely do not need to do it either. Because if 3rd Parties don't even think it's worth their time and they can't make any money off of it... why would we possibly think it'd be in WotC's interest to do so? After all... why did WotC suddenly decide that making a Bastion system of all things in the 5E24 DMG was now worth it? (Something they never really bothered with in the 3E, 3.5E, 4E, or 5E14 DMGs?) My guess would be because they saw how well MCDM's 'Strongholds & Followers' book did in the market, and showed there might actually be a true desire for stronghold systems like that.
This is the same issue with so many other things that people say that the game needs to have-- Warlords, Psions, Arcane Half-casters, species point-builds, etc. etc. etc. No one is actually proving to WotC that any of this is true by going to a 3rd party and all using one of them happily and in large numbers. They aren't showing anyone at WotC there's a true market for this stuff. But if WotC could actually see that there was a market (because everyone kept using and/or talking about 'X' 3rd Party version of The Warlord for example)... WotC might be more inclined to make one of their own.
But of course that's just my opinion. I could be wrong.