Why don't some animals have vestigial structures?

Vestigial structures are structures in the body that no longer serve a purpose but the organism has not lost them through evolution because the feature doesn't harm the organism.

In other words, it's a structure that used to have a purpose but doesn't anymore, so it's kind of just there.

Therefore, some animals don't have vestigial structures because they never lost the purpose of that structure. If it still serves a purpose, it can't be vestigial.

On the other hand, the feature could have become detrimental, meaning it caused the organism harm, in which case, over time, the species would evolve not to have them anymore.

nucleus

would be most reasonable answer tbh