>>40893387 (OP)
if i had to guess, it would probably have something to do with late stage empires syndrome.
In early empire, you have the "strong man" who unites the various city-states/provinces, with ever widening border expansion of neighbors. Eventually this dynastic force runs out of steam, and you begin to see the young emperor+Dowager Empress+eunuchs bureaucracy union. Similar situations happened in China, Egypt, Roman Empire, Mesopotamian, etc.
It's a way for the mother/female to acquire power in a male dominated world. Not sure if it should be seen as in opposition to early empire male strong man and thus a male vs female motif, with females always ushering in demise, regardless of government type.