@calebelijah
Both Bertia and Heronia seem to know what happen in the prince's bad end. While all the other capture targets have their consolation prizes for lack of a better term, the prince in the game was stuck with evil Bertia, and him not marrying the heroine would be a bad ending because of that.
If I had to guess, it would be because the prince in the game's setting seemed to be a cold and calculating person. Had he married villainess Bertia without ever experiencing "true love" he would have tried to fill the void with war and tyranny. The guy is too much of a genius for his own good, plus before meeting our dumb villainess, he also lacked empathy. Not a good combination for a ruler.