I agree that COH could have benefited from more advertising, I think it needed to be the right advertising for the right audience.
The most effective advertising pushes are going to be tied into a new launch, or a re-launch. Perhaps they could have done TV or movie commercials to promote Freedom, but even if the budget was infinite, there still needs to be a return. If it costs $5M to get a trailer to show before a movie, will you make more than $5M in subscriptions/MTXes by showing that ad? Especially if you can't guarantee that your audience even knows what an MMO is?
Maybe if you're a World of Warcraft, with hundreds of millions of customers. Or if you're launching a major new console game. But for an 8-year old game, it's hard to rationalize that high a return for such a huge investment. People generally want new things.
This is one of the reasons why you see things like banner ads, site takeovers so widely used. Not only are they cost-effective, they tend to target the general demographic you want playing your game.
I think if we did see COH commercials on TV or in the movies, it would make us as players feel better, but I don't really think it'd have as big an effect on the game itself. I think there's other forms of advertising that would be more cost effective.