Future expansions.

Well, there shouldn't be a particularly complex story about escaping from the mages – only Goblins remain of the beastmen. It's harder to explain why they, like the Nagas and Faceless Ones, disappeared by the time of the fifth installment. And personally, I don't like this faction – even the name itself is off-putting.

The reason is not complicated. Considering who we want to pit them against, the conclusion is: the Swamp and Sanctuary are irreconcilable enemies (we already know how it will end, but the main thing is how), and the Faceless Ones benefit from their feud for their "certain" plans.

Has anyone noticed that in the editor, in the list of factions, when you choose one for the player, the Academy is present.

I think the developers initially created a large number of cities (factions).
But in order for each to have its own unique characteristics, time is needed, which they don't have. This is a marketing ploy. They release a game with only a part of more or less playable factions. While we are enjoying the sixth Heroes of Might and Magic, they:
-make money from the release
-fix the shortcomings
-develop a more or less playable add-on
-make money from the add-on
-fix the add-on
-develop a more or less playable second add-on
-make money from the second add-on
-fix the second add-on