the big companies like Janiclean (i think, its Jani something) get a contract and they sub out the actual work to independent contractors.

Know a guy from my town who had a history (prison, drugs) and started his own cleaning company. Not indoors, but outdoors. He does small shopping centers, grocery stores, medical buildings, etc.... Trash cans and parking lot. Can start small on your own then build biz up. He's running a 6 or so trucks now and makes bank. Funny thing, he now has a parking lot contract with the State prison where he served time.