YouTube copyright encourages original content or content your allowed to use. If you use content your not supposed to. You can recieve a copyright strike. These laws are set in place to protect the users and makers of their original content.
If you want music you will be allowed to use. Look up "NoCopyrightedSound" on YouTube. They have a large selection of songs you can use for your content without needing permission because they keep their content free to use. If you want good thumbnails try using cropped screenshots of your content in video. Or let's say you make a video of graal chest. You could get creative and make video thumbnails like you holding a gralat in the air as you got a chest or ect.
You can't blame copyright laws though. If there was no copyright laws TV shows, Anime,Music.ect could be redistributed by anyone and no one could make profits on their own content. For instance let's take Naruto.
If there was no copyright laws. I could post every naruto episode ever made at best quality and audio and paid for it. Did I make it? No. If you ever see a naruto or other anime thing online it's usually nonprofit. Only way you can make it profitable is if you edit it in some way to make it drastically different. And even that is iffy