Most of them are ripped from Guitar Hero/Rock Band, because the games needed to mute individual instruments when you were not playing the correct notes. (With 10+ games and lots of DLC, there's actually a lot of songs that were included)
There was also a service called jammit marketed to musicians where you could buy multitracks from their partnered artists. There are also artists sharing them in deluxe editions of albums, for example I think Dream Theater did it for Black Clouds and Silver Linings?
There's also the possibility of just knowing someone in the industry that could have access to them, maybe? I know Rick Beato who does song analyses on YouTube is a producer, so he could get some this way.
There was a great channel on YouTube dedicated to sharing these isolated tracks called digital split, unfortunately it got banned from YouTube twice, so I don't think it's coming back...
It wouldn't surprise me if popular channels got access to the raw tracks from the studio (for whatever the normal license terms are to use the full copyrighted song in your video - a share of the advertising).
Popular is key - you need to get popular doing analysis of work nobody has heard of first. Once you are popular on YouTube everyone wants you to advertise for them.
There was also a service called jammit marketed to musicians where you could buy multitracks from their partnered artists. There are also artists sharing them in deluxe editions of albums, for example I think Dream Theater did it for Black Clouds and Silver Linings?
There's also the possibility of just knowing someone in the industry that could have access to them, maybe? I know Rick Beato who does song analyses on YouTube is a producer, so he could get some this way.
There was a great channel on YouTube dedicated to sharing these isolated tracks called digital split, unfortunately it got banned from YouTube twice, so I don't think it's coming back...