I Gave Up on Conquering the Heroines

For unknown reasons, I found myself in a game and am on my 12th attempt at clearing it.
It appears impossible to achieve the “conquer all heroines” ending.
The moment I decided to give up on conquering the heroines and aim for the “defeat the final boss” ending instead:
[The monsters in the dungeon are strengthened by Saintess Jill’s blessing.]
[The monsters in the dungeon gain weak toxicity due to Witch Yulia’s curse.]
[Cold air envelops the dungeon because of Frost Lord Yerina’s grudge.]
The heroines started blocking my path forward.