“If this video is infringing on copyright (and I don’t believe it is) then why is YouTube not taking it down?”
Did you yourself compose this song? If you didn’t, did you purchase a Master Sync license allowing you worldwide broadcast rights via the Internet? If not, your cover is infringing; and the first thing you should do, is check the video’s listing in YouTube Studio to see if the ads are due to a copyright claim. If it has been claimed under Content ID, you have the answer to your question of why it hasn’t been taken down.
The copyright owners have chosen to monetize it for themselves instead.
“I am also not re-using any content– -unless my showing how to play a recorded guitar solo (using my own backing track) is regarded as re-using.”
Please refer back to the first part of my reply; as if you aren’t the composer, you’re reusing someone else’s composition even if you did record the backing track yourself. Compositions have their own separate copyright which is distinct from from the copyrights for Master Recordings or live performances of the song.
(I’m a Royalty-Free and Commercial music composer in my own right)A channel of tutorial videos like that one can probably be made monetizable, once you get the required number of subs (1,000) and watch hours (4,000 in the past 12 months) and pass the review. However, you also have play-along videos on your channel. Those would make the channel non-monetizable (and are definitely copyright infringing).You also have videos with copyright claims on them. Those would make the channel unmonetizable. If you are looking for monetization, you probably need two channels. One for tutorials and originals (the monetizable one) and one for other stuff. However, even with the tutorial channel, you will likely get copyright claims that you will have to deal with.