Where are these Rules anyway ? I can't seem find them.
Type in google "Youtube's community rules". It should have a list of things that are not allowed on Youtube. Back then, I had custom music that was copyrighted by another artist because the particular song is licensed or advertised that gives them money in the first place. So for example, someone makes a video and they upload it that provides them ads and revenue. You upload that same video of his but you get more views and money out of it while the original person didn't. This is against the rules because you are earning money and views for something that you never made or own, so you are getting something free for something you didn't do.
Music is the same thing here. Only way to bypass this is if you ask for permission on his/her side, which I did get permission, however the person who owned the song completely licensed it worldwide soon after, so the song can't be used on Youtube and gave me a copyright strike. Now with the internet and Youtube improving, they've developed a way for the person who owns the content from people who uploads their stuff or uses their music to get revenue out of it. Before, that was impossible.