Welcome!

Flying is still safer than your other forms of transportation. Airlines operate under strict rules and systems governed by minimum equipment lists. If the item is on the list, no matter how seemingly minor, it's a no go. Wipers cannot be inoperative when there is precipitation within a certain distance from the airport. Unlike off the shelf wipers and wiper motors for automotive use, the parts used in planes must be thoroughly tested and approved for aircraft use by the FAA. Likely the part was not in stock and maintenance couldn't just run down the street to pick one up from a store. In your personal car, you could simply disregard and drive on. As an additional detail, I have heard from a friend in aircraft maintenance that Delta is still trying to integrate with the former Northwest when it comes to repairs. Lots of little issues with parts availability at operating bases.

Just a few weeks ago, I was on a flight delayed an hour because of a burnt out bulb for a warning light in the cockpit. The audio warning still worked and the plane legal to fly but the Captain elected wait for a replacement bulb. Rest assured that flying is still very safe compared to other forms of transportation.