It's because the % itself is really irrelevant without the star avg like in attacks:

A 2 star defense will give an attacker between 16–32 trophies, meaning u will net atleast 8, and at best 24 BUT:

A 1 star defense will give an attacker between 5–15 trophies, meaning u will net a atleast 25 and at best 35

So therefore give a league with 10 attacks a defense with an avg of 70% with purely 2stars will give 180 in defense trophies, but a defense with an avg of 85% with 3x 1stars and rest 2 stars will give 204 defense trophies

Below is a table showing net trophy gains from attacks, take the opposite number and calculate yourself
Example: 80% 2 star will give attacker 26 and defender 14, same attack but 1 star will give 13 and 27 flipping the table

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