There were probably many reasons, but it appears it was to undermine the authority and veracity of the papacy, to cast doubt upon the traditions, practices and beliefs of Catholics down through the ages.
It also prepared the way for bigger, better changes. If saints can be made one day, and "deleted" the next, then the sky's the limit in terms of what can be changed or altered. And the authority that approved the cult of St. Philomena, St. Christopher, etc., is not worthy of being followed or believed. Nothing is sacred. Nothing escapes modern "progress".
It was also motivated, i believe, by a general hatred of all things Catholic.