D.V.
Two things to evaluate.
Pull ups are just too comfortable. Pullups delay potty training because they can't tell they are wet.
Sometimes this happens because of either food allergies, or vitamin deficiencies. ( ususally B vitamins) Any easy way to determine if food allergies are the culprit is to observe if there is a specific food they are craving.
My daughter, it was apples. Apple jack cereal, apple sauce, cut up apples, apple pie, etc etc. One of my friends, it was a sensitivity to food colors and additives. Hotdogs have the red, Kraft Mac & cheese has the yellow etc.