HeavyMetalGamer : Gone are the days people would post a vid of their pet doing something cute. Now YT is a full time job for some people and they often turn to crowdfunding to help cover expenses. You are right,YT is super overcrowded,and it is tough to be unique in a bunch of "me too,me too"  channels. Not to mention,YT is cracking down on people who post stuff that does not meet guidelines. A few years ago,they did not give a rat's @$$ about it. Now you have competitors like vimeo.com where the terms are not as strict and people are starting to pop up there. I watched a Robocop parody on there that they could not get away with on YT>

Oldschool777 : When you say you don't understand why Markiplier is popular, either you're trying to be obtuse on purpose or it's so big and obvious, you're just missing it.

Markiplier is popular because he is (a) attractive, (b) friendly and conversational, (c) confident about himself, (d) able to handle humor without being over the top, (e) emotive and people enjoy seeing emotions, like screaming for almost no reason.

The biggest reason is he interacts with the fans. He generates content based on their comments, based on what they say and what they want, and he doesn't just do what he wants to do. I'm sure he can't email 10 million people at any given time but he takes a majority of subscribers, talks to them or at least at them, and gives them an experience. He thanks followers for following him, he acts humble about his success, and he tells the truth.

I'm baffled that you miss that. You don't have to like the guy, heck you can hate him, but you have to see why he's having success.