It would be different if they asked him to do it and agreed on a price beforehand. Maybe it would be smart business for the company to offer some better incentive for him to keep the video up so they can continue to make money off it. But they certainly don’t have any obligation to do so.You guys are amazing! Come on, when I read they send him 3 t-shirts I wanted to laugh so hard. I would be more than happy if someone takes my content and take it into millions of views to share money even 50 - 50%. If they have on the original channel also many views it will be fine to send you nothing, but if your video is having more interactions then I would say you definitely deserve something for that good marketing. You people are so negative with the comments. Try to be more realistic if you are in his situations. I would also expect something.
Example to clear your heads even more: Amazon, Aliexpress, and all big players will give you around 8% of each sale if somebody buys some item over your link. That is natural because they sell more than they would sell without you. Same applies to these musicians, they became more famous because of him uploading their music, maybe they will not be discovered soo much without that his upload. People pay to advertise on youtube, and they got a super good advertisement on youtube and they are sending 3 (THREE) t-shirts. Amazing how some people are greedy.