The masteries for the two new civs do not have the same amount of historical descriptions and factoids that the previous eight civs do. It was a pleasure doing the masteries for the previous civs and learning lots of new facts about each mastery throughout the process. I request that something might be put together for the new civs too.
Two weeks ago i have do the same question in a post:
I only suppose that the designers are waiting to see if the Malians and Ottomans are enough powerful or become very weak and need a buff as another unique tech or new units. And until that they dont gonna put all the masteries of those civs.
The other possibility is that they are planning a campaign that includes one of the 2 new civs, and so that the information of the short facts is not crossed with the videos that they will make, they have not put all the data.
The last possibility is that they really wanted to put the “Akinci” or the Ottoman horse archer, but due to balance or lack of time to design the unit they did not do it, and in order not to put it in short facts they are still considering which short facts to put.
Finally, it could be a design error, and they forgot to activate the short facts of the new civs for challenges other than tests of power 1, 2, 3, 4.