Why didn’t Ganon rule Hyrule forever? *spoilers*

In the intro to the series before every episode, Zelda states that whoever gets both triforces will rule Hyrule forever. But there was an episode where Ganon was able to get both Triforces, before Link and Zelda were able to get the Triforce of Wisdom back. Why wasn’t Ganon able to rule Hyrule forever when he got both Triforces?