You brought up some great points but YouTube is not a good platform for a publisher to sell ads since most of the revenue goes to Google.
I'm a little confused. Here's how it goes. Pretend MM&FF had a YT channel, and a half million subs. Every manufacturer would be begging to have their parts featured. Say MM&FF is driving down to FL to cover a race, vlogs the race but also the drive down and mentions how great their new Koni shocks make their 2003 cobra project car ride. That means Koni probably gave them the shocks for free, and maybe even made they to drop the mention. The more views, the more income MM&FF gets, the more sponsorships they get offered, the more content they can produce, the more views, the more money, etc, etc.
A big automotive YTer just talked finances in a recent video. With his GT350, he paid 53, has spent 4K on it, so 57K, but his 18 videos on it has made 48K. The car is worth maybe 40K at Carmax, so that's a 32K net if he dumped it today. That's just ONE of his many cars.