Thema and Platonism

Hello Rabbi, I’m watching your video series on Platonism, I really enjoy it.
Today we learned in a morning seder that there is a method in Rabbi Yehuda’s mishna that says that there is a half-dead half-dead bull. The Rashba there asks, so how can he pay a full ransom? If you understand it simply, it is half-dead and half-dead, and he excuses himself that the Torah required that because of the half-dead bull, he pay a full ransom.
It reminded me a lot of what you said about a woman’s halal. Here too, there are two objects about it: a festival and a tam, and therefore the Torah is binding on the festival side of it.
But my question is, why are we obligated specifically according to the festival side and not according to the death side, in contrast to the example you gave about a single woman and a divorced woman, where the Torah says that a divorced woman is prohibited from marrying a priest, but a single woman has no prohibition and no obligation, and therefore we will follow what the Torah says, but here in both cases the Torah says that he is obligated only that according to the death side he will pay half the ransom and according to the festival side he will pay the full ransom! So why shouldn’t he pay if he already has one and a half!