Any number of things could go wrong utterly invalidating the release conditions
Probably on purpose out of spite, that's my guess. The fact that a guy exists who could actually break it was most likely not accounted for.
The characters all acting like he has to
pick supports the idea that translating it as "marry all of the princesses" was a mistake. But that's probably the point; that IS the release condition, but reaching that conclusion without harem manga knowhow and actually going
through with it is unlikely. Remember that the original prophecy didn't clarify that there was more than one "Princess" either. The Witch wanted an impossible game, too many challenges for a wannabe hero/suitor to bother with.
I don't see this manga going the "pick the favorite" angle. The girls clearly highly value each others' happiness (to the point of playing wingman for each other), and resolving things with the Witch will also be important. Quite a lot of progress has also been made in a single month out of the entire year. The collective himbo husband IS the endgame, the main issue is for the girls to beat the real final boss; MC density.