Air carrier ground personnel reported finding excessive amount of oil in the front belly of the aircraft.

Narrative

My crew was assigned to work a flight on [gate] XX when we arrived my belly worker attempted to get into the front belly. She slipped and fell due to the oil. My second person got in finding oil in the entire belly. Another crew offloaded and did not report it there was so much substance that it was on the belt loader too. I notified the captain he did not want to report it until it got to the destination did not leave flight deck to see it even. I then notified management Person A was sent out to see. She observed all the oil and her boss told her to take paper towel into the belly and clean it up. I expressed to her multiple times that that it could be hazardous and she should not be doing it but she did anyway all of our training we should have had a hazmat team clear it. No one was called they had another crew come out and load it due to it being time for us to go home. Cause: Oil leaked in belly previous crew spread it through entire belly and on the belt loader. Manager tried to clean even though i told her it could be hazmat due to us not knowing what it actually wasSuggestions: management was in such a rush do get plane out that they ignored rules that we have in place for something like this.