gender pronouns are often used to mean pronouns.
Not everyone's gender has a relationship to the pronouns they use to identify themselves. Some people are agender or gender non-conforming and still use pronouns.
Reiterating "gender pronouns" enforces the idea that there is necessarily a relationship between the two, and furthermore, it can suggest that if there isn't a relationship between the two, that it is not a valid use of pronouns.
By connecting gender and perpetuating unnecessary gender norms and expectations, we are perpetuating violence against gender minoritised people. Using this language perpetuates those systems and language of harm, regardless of our intent.