Princes without control, princesses without chains
What if the princes that remain today are those who accepted their arranged marriages while the adventurers with a rescue complex became extinct after bothering enough princesses?
Perhaps they finally got tired of seeing their naps interrupted by unwelcome invaders giving unwanted kisses. Perhaps the promise of power, gold and bloated garments stopped conquering them. Maybe the "but I'm charming!" stopped sounding like a good excuse not to put out a restraining order. Perhaps those egomaniacs on the throne of the world were finally arrested for selling cheap stories.
Or maybe....
Maybe they allied themselves with their dragons. Perhaps they discovered that this power to spit fire and shake the earth was in themselves. Perhaps they reclaimed their nature and admitted that they could want to fly free and make their roar heard without ceasing to be polite and delicate like flowers if they wished.
Perhaps they finally got tired of having to wait until someone else rescued them to see their lives finally begin, and they preferred to go out and fall in love during the adventure, forming part of it and riding with their princes as conquerors instead of being the prize after the conquest.
And who knows, maybe they lived happily ever after.