Considering how widespread Uber is, it's probably got a formula for opening up new offices in new locations. I know other companies I worked for had one so I can only assume Uber is the same. This is they know they need 2 x, 3 y, 1 z. Managing a series of contractors at that scale for each location would probably be a job by itself and kind of remove the benefits of outsourcing. Considering Uber literally deals with high turnover of personal by the nature of what they do, they don't seem like they would be likely to be that risk adverse to the paperwork challenges that potentially could come from low level staff like cleaners which is normally why companies prefer to outsource it. Like if your used to hiring office staff where high turnover would be employees leaving after a year vs cleaning staff where staff could change on a monthly basis, the hassle of dealing with paperwork isn't worth it. But if you've already got the person who deals with the paperwork, etc because that's your business it's less of an issue.

I think it's very likely Uber employs cleaners themselves due to costs attached to outsourcing and that they already have the staff to manage that sort of worker.