I don't think the troubles (and arguable decline) of internet reviewers as we know them are caused by any one issue, but I'd gamble that the excessive personae and "storylines" put an expiry date on a lot of these people.
Basically, money and popularity by the sheer numbers provided by the internet aren't good enough for these people, and reasonably so. E-fame conceivably isn't the same as "real world" fame as an entertainer because the tangible influence of the internet famous is usually limited to a niche (if we're talking physical spaces: conventions) and besides the intense competition, fame on the internet naturally comes and goes very fast. So it follows that so many of these critics have ambitions to extend their territory into the "real" world: making films, aiming to score TV appearances, etc.
Of course, when their internet personae and storylines (which tend to be impenetrable to anyone other than their more loyal fans) have a symbiotic relationship with their humour and criticism (which could otherwise stand alone) it makes them harder to access for anyone in the "real world" whether it's an audience or an exec deciding if they're gonna be on TV. Like Arctic is suggesting, I think this in part explains James Rolfe's continued success: he has a talent for drawing a line between James Rolfe and the Angry Video Game Nerd.
Lots of critics, especially CA folks, don't have those social skills and theory of mind. Additionally, they might not realise this, but they tend to know when their efforts to venture into the sunlight aren't working out, and this makes them slide deeper into their niche.