Why is there a glut of ecchi themed combat school anime's where the main protagonist immediately offends the main female lead and then must duel her to save face?

I believe I have seen 4-5 anime's with this beginning premise and I'm now watching a new anime, Hundred, with the same theme. Sometimes it's a school of magic, or a school where students pilot mecha's and enduringly the protagonist stumbles upon the female lead naked or simply offends her and is challenged to a duel, why is this specific premise so incestuous among anime shows and so recently at the same time?Edit: I understand it sells, but the deeper question is why do the anime houses and the writers so blatantly copy each other so shamelessly, does this happen a lot with such specifity? http://ift.tt/24qBSuf