Comment by DoctorOetker

There is a difference between a new monarch 1) letting a symbolic but insignificant fraction free to gain popularity / manufacture consent for the governance of the new monarch 2) clearing out all the prisoners.

Symbolically different alliances/parties fight each other, but within one such party/team the partners are competition too! Why liberate an old partner, if that increases your commpetition? Often the strategic value of this partner was low as the prisoner has been out of the loop, destabilized, broken. Automagically everyone agrees that "agitators are agitators" and a large fraction of the populace already believes whatever the political prisoner was accused of by the previous government.

Regarding petty criminals and the "expense" of housing prisoners, that story really gets old very fast to be honest. Although seldom depicted in caricatural movies, we know historically there were no dedicated mental institutions. In the past they locked them up with normal criminals, no distinction. And they did forced labour like textile industry, like proto-factories. From the perspective of government thats an income, not an expense!!