Two possible reasons.
1. Your windshield has an oily residue. You can use the kitchen cleaner to clean them off. clean with a high-pressure hose to the outside of the windshield( not necessary inside).
2. The film on the windshield is possibly aging. You need to use a professional oil residue cleaner to clean it and then apply a protective coat to it. (probably fix it at a shop) or repalce the film for a new one if it has aged completely.