There are many small countries in Europe that manage to survive and thrive, each with its unique way of living.
Now that Prussia has fallen from the ranks of the great powers, to live comfortably without constantly receiving a social thrashing, it must abandon its previous ways and learn the survival strategies of small nations.
Frederick III was very clear-headed, "The merger of Prussia and Hanover to establish North Germany, integrating the many sub-states of the Germany Region and controlling this new nation to rejoin the ranks of the great powers," was just a fabricated lie to cheat naive youths.
In this era of survival of the fittest, without strength, you are nothing.
The Kingdom of Prussia, having lost the region of Prussia, had greatly diminished in strength. To dominate the situation, it first had to consider whether Hanover would agree.
The Kingdom of Hanover, having acquired territory, had overtaken Prussia in terms of overt power, especially in economic advantage.