Didn't Big Brother have pretty much zero sponsors this year, obviously outside of Ambi Pur and KFC? Oh, and Appliances Online, but I mean... that isn't Holden (or whoever used to give out the cars), so.
I think a lot of former HM's can demonstrate they can generate interest and income from advertisers. They do much better than people who go on The Block expecting fame. Of course a big name brand isn't going to be handing out cars if it is on at some random time at night and gets rescheduled constantly.