Also they may recycle or reprocess much of the waste themselves, or have contracts with reprocessers. Forex: used lubricating oil is not irretrievably soiled - rather it’s got entrained contaminants in it. There are a number of ways to remove those contaminants safely. (Usually simply passing the waste oil through a lube oil purifier would do the trick.) It may be more economic to use it as a fuel, but it’s not the only option.
Similarly, while it’s prohibitively expensive for a reprocesser to pick up things like NiCd batteries, if they’re concentrated in a central facility, they may become an economic viable source of material.