Magic is awesome, except when it just makes everything worse. It happens rarely, but sometimes magic as a whole is a net evil thing in a story. In order to bring, well, order, back to the world in question, magic has to go. Although it’s sad for both the characters losing their magic and the audience by proxy, by casting fantastical power as something that’s fun or useful but ultimately damaging, these stories can teach us something worthwhile about the importance of self-sacrifice.
Spoilers for the entire Young Elites and His Dark Materials series below the jump.