I suppose it matters whether YouTube content is hosted in these USA or outside of it, for purposes of international copyright.
I'm not really sure how it all works internationally, but I know that on a site such as Wikimedia Commons, which is 100% hosted in these USA, they are still mindful that every work they host is 100% free in all involved countries. So if a more generous Italian copyright, say, or an Australian FOP law, gets in the way of hosting an image, they will always respect that, rather than relying on the technicality that the image is only hosted in these USA and they don't strictly need to observe other nations' laws in that regard.
YouTube may have distributed content hosting in other nations, and so I don't know how they get along with international copyright, where as you say, fair use is less fair than in USA. Perhaps they do rely on hosting location as a definitive test for which laws they're going to obey.
I'm not really sure how it all works internationally, but I know that on a site such as Wikimedia Commons, which is 100% hosted in these USA, they are still mindful that every work they host is 100% free in all involved countries. So if a more generous Italian copyright, say, or an Australian FOP law, gets in the way of hosting an image, they will always respect that, rather than relying on the technicality that the image is only hosted in these USA and they don't strictly need to observe other nations' laws in that regard.
YouTube may have distributed content hosting in other nations, and so I don't know how they get along with international copyright, where as you say, fair use is less fair than in USA. Perhaps they do rely on hosting location as a definitive test for which laws they're going to obey.