Here's why:
* Costume Variety: Glee characters, including Rachel, were known for their diverse and often outlandish outfits. While skirts were a part of Rachel's wardrobe, she also wore pants, dresses, and other clothing items.
* Character Development: Rachel's character arc involved her evolving sense of style, from her initial focus on classic, feminine looks to embracing more mature and individual expressions.
* No Official Statement: There's no official statement from Lea Michele, costume designers, or producers indicating a deliberate decision to only have her wear skirts.
It's possible that the idea of Lea Michele only wearing skirts originated from a limited recall of the show or an emphasis on certain outfits that stuck out.
Ultimately, Rachel Berry, the character Lea Michele played, had a varied and diverse wardrobe on Glee.