The video (a bit over half an hour) was pretty good. It was an interesting overview of the game, it's popularity with many players, and the timeline over which it was active. But, in the end, it wasn't really a convincing explanation of the death of the franchise, as the narrator honestly notes himself.
Some of the factors were mentioned. There was a decent explanation of how COH/COV could be thought of as a burden BY NCSoft, even though the game was not losing money at that point. A company like that has to think in terms of where to maintain resources. Keeping a studio around just to maintain an 8-year-old game that was 2% of its revenue when it had large plans for other major MMO game releases would be a decent reason for NCSoft to want to close up Paragon Studios and end COH/COV. And, on top of being a small revenue generator for NCSoft overall, COH/COV never got much traction among gamers in South Korea, which was NCSoft's home market. The knowledge that a significant investment would have to be made to modernize the game's engine was probably another strike against the franchise.
However, the central question of why not sell COH/COV to Paragon (or the others who might have been interested in purchasing the COH/COV IP) was never really addressed. One gets the impression that, without more inside information from NCSoft, we just won't know the answer to that question, though many explanations are plausible. Maybe the potential buyers just weren't able to come up with enough money. Maybe NCSoft wanted to keep the IP in case they wanted to get back into the superhero MMO game business in the future, particularly if one or both of their other 2012 MMO releases underperformed. Maybe the IP was connected in some non-obvious way with other games NCSoft had in development. In any case, we are left without an answer.