The Room isn't that bad in comparison, but it's a special kind of bad that you want to share with others. Also, when people learned more about Tommy Wiseau it added to the fascination. Manos (and Birdemic, which should've been in your marathon) have had articles written about them, but their behind the scenes story isn't as fascinating. Manos was also the perfect film for the MST3K/Rifftrax treatment, because they can build a lot of running gags to fill the dead spots. Manos is a far harder film to watch without them. (If you watch the Rifftrax ep of The Room, it's comically beating a dead horse and the hosts treat t more like a Rocky Horror experience.)
Neil Breen is a whole other level. The incomprehensibility of his scripts, filled with him clearly being passionate about something, is rendered worthless because he has no charisma, no personality, and even after 4 films there is no hint that he's in on the joke. The little that is known about Breen, the less people care, which doesn't add anything to the enjoyment of his films, which seem like they would be brutal to sit thru. (I've only been able to watch a few clips.) There's a thread on How Did This Get Made because people want the podcast to do a Neil Breen film, but it's been nixed because there's no fun and they don't want their listeners to feel obligated to watch in order to follow the show.