A deleted scene from Wicked explains why Glinda can’t perform magic in the movie. The story of Wicked follows Elphaba and Glinda, who eventually become known as the Wicked Witch of the West and the Good Witch of the North, respectively. Wicked follows Elphaba and Glinda as they form an unlikely friendship as students at Shiz University. In Wicked, Glinda is immediately jealous of Elphaba’s magical abilities, as she can’t perform sorcery herself. This is interesting, since Glinda eventually becomes a highly respected witch in the world of Oz.

https://screenrant.com/wicked-glinda-cant-do-magic-deleted-scene-explainer/