I've seen a youtube video quite long ago about this, basically it was saying that YouTube is getting money from those channels with ads, as with any channel and they are trying to get away with as much as they can, so as long as nobody really reports or copy claims them they stay up and running.
They could edit some minor things like the sound, flip the video and add distortion/noise, zoom in the video and some tricks to avoid the initial copyright check.
These accounts will be terminated eventually, they won't stay active forever.