Bob can blame the algorithm all he wants, the fact is that his downfall has been predominantly his own fault.
(I'll start with a caveat: YouTube's algorithm is notoriously obtuse and awful, and it's a lot of guesswork as to what will get your channel promoted. The latest thing seems to be pushing Shorts on people, but even then, as Bob found out, you still might not get picked up. So while I'm still laying most of the blame at Bob's feet, YouTube doesn't make it easy.)
For starters, Bob has squandered basically every opportunity that's come his way. He got in on the ground floor when the idea of posting your own reviews online for others to watch was just getting started, and he managed a decent following and consistent views talking about both movies and video games. However, he let his personal channel flounder as he got hired by one site or another, until either he got fired or the site shut down and he moved on to the next, but in the process his channel stopped getting recommended to people. In between jobs, he had his Pixels review go viral, which he could have used as a springboard to go freelance full-time, but he wanted the "prestige" of working for a bigger name and thus didn't capitalize on it, making his channel languish further. The result is that he's basically entirely on his own now, only in a much worse position than he'd be if he would have focused more on his solo efforts before.
Another issue is that Bob refuses to collaborate with anyone else for some reason. If you look at a lot of the bigger YouTube channels, they're either group efforts or they're solo creators that frequently reach out and collab with other channels. That networking allows for viewers of one personality to find others that they might enjoy as well, because if the person you're watching likes this other guy, then you probably will too. It's likely that this is also part of how the algorithm will recommend channels to you.
Bob doesn't do this. Sure, he'd say that he collaborates with the Theorist channels when he skims Wikipedia for them, but that's not even close to the same thing. Bob doesn't have discussions with other YouTubers, Bob doesn't work on videos where he and someone else play a part, he simply keeps himself confined to his own little bubble. The most he's done is the occasional discussion with his brother, but that hardly counts. Hell, when YMS offered to have him on for a back-and-forth about something (I think it had to do with not finishing a movie before reviewing it, though he clearly stated as much), he firmly declined because, hilariously, he thought that YMS was trying to ride his coattails (never mind that he has 10x the subscribers).
And that leads me to his other major issue: his attitude. Bob clearly feels that success is owed to him, not from anything he's done, but simply by virtue of who he is. He believes himself to be an ubermensch that people should be listening to, praising even, and the fact that they're not clearly means that there are forces conspiring against him to keep him down. In this case, it's not the many things he hasn't done to support his channel, it's that damn algorithm. And he states this all with a wholly undeserved smug sense of self-assurance. His ship is gonna come in any day now, just you wait, chuds!
Rather than do some soul searching and realize that it's his negative demeanor that's causing his problems, he wallows in anger and rage, shouting impotently into the void at all hours of the day rather than working to improve himself. Of course, what else can one expect from a man who brags about deliberately sabotaging his therapy sessions when he was a kid? This is a man who will never actually get the help he so desperately needs, because he's too dumb and stubborn to take that first step.
And as much as he prides himself on not pursuing the "angry reviewer" route post-Pixels, it's clear that he really didn't have to. RLM first got mainstream attention through the Episode 1 Plinkett review (a mild form of "anger" tempered by excessive drunkenness), but they built an audience through their standard yet humorous new movie reviews and later branched out into other review formats (old B-movies, random VHS tapes, old movies they enjoy), to the point where they can put out random trivia shows and still get people to watch. YMS started out with longer teardowns of bad movies (hell, his channel is short for YourMovieSucks), but continued to maintain his audience through current reviews in a more toned down nature, as well as attending film festivals and getting word out about movies that his audience might not know about yet. And we can't forget about the anti-Bob, Critical Drinker, whose angry drunk persona gradually toned down to the point where he's generally just bemused by how bad a movie is rather than actually pissed about it, and he's even a published author and in the process of producing a short film based on his works.
What do they all have in common? They stuck with their channels and put in the work, they collaborate with others in a variety of ways (whether it's having guests on their shows or doing livestream discussions with fellow creators), and they maintain a fairly positive attitude. They've all had their missteps, but people continue to watch because above all, they remain entertaining.
I wrote a lot here, so apologies if you decided to read it all, but to summarize: Bob, you are your own worst enemy, fucking up your potential success over and over again. You lucked into this gig early on, but what worked 15 years ago just isn't going to cut it these days. Either learn how to do this shit properly (you can't even chroma key right, for fuck's sake!), or quit.
build, Believers 
