Well, I think there are two issues here about what you mention. One being that a such you think "let's plays" and comments over cut scenes are lame, there is a market for it. People want to watch it, to the tune of millions of viewers.
One of the larger issues is the YouTube filter system targeting things that have been cleared as okay for a long time. Things like royalty free music that has been declared free to use by the composers is suddenly triggering take downs and flags. Game devs that have long declared their games okay for videos and streaming are having to tell their players to immediately contest any flags from YouTube because they have no clue what is going on. Some devs rely on these videos as a means of continued free advertising for their products.
There is also the question of YouTube's process. It's as if anyone can file a copyright claim without having to prove the content is really theirs, and YouTube will immediately flag or take it down. It's a tirade I could go on about at great length that includes conflicting case law about copyright infringement, but for now I will say this is a giant mess.