Why Caponata Recipes Call for Wiping Out the Pan

I have a recipe for caponata which I love. There is one step in the recipe which has always puzzled me.

The first step is sautéing in olive oil the onion and celery , then adding the garlic. Then taking it out of the pan to hold it. Then sautéing the eggplant in olive oil but (this is the piece that puzzles me)

The recipe says to wipe out the pan well before proceeding to the sautéing of the eggplant - this seems unnecessary as they are all to be eventually mixed.

Am I missing something ? Why this ‘wipe out’ step ?

Thanks