If they were to reclaim Earth, then the whole concept of the Twelve Great families would surely decline and one day collapse.
That was a future they couldn't accept no matter what.
Thus, they sort to maintain the status quo now and even expand their reach further.
Of course they still sent their offspring and seed to the academy, as a public show of solidarity and to also train them.
But that was all an act, after all, the moment their offspring graduate from the academy, their families would immediately call for their return, with very few allowing them to actually embark on missions to the blue planet.
Using the guise of making them family guards, they were casually building up an army to oppose the might of the Guardian, right under their noses to be precise.
Alas, those on the Guardian knew this but couldn't do anything about it and could only watch as their resources were expended training those that could end up biting them.
