This past December, YouTube flipped a switch that instantly caused havoc with anyone trying to make a better living through video. The change caused their Content ID system to go on an aggressive rampage which left a huge pile of (erroneous?) copyright violation take-down notices in its wake.
Gaming videos were particularly hard hit, including those that were part of sanctioned channels – in other words, people who were given specific permission to do what they do, were slapped for doing what they do. Since removing every potential violation would have left YouTube looking like the shelves the day after the day after Christmas, they resorted to simply removing the monetization option.