Free to Play (F2P) is not a cure all.
City of Heroes is currently scheduled to go dark later this year. There are many efforts underway to try and prevent this, and I won't knock them because there are a lot of people who really liked this game even if I didn't when I gave it a shot. But, I won't pretend they are likely to succeed either given that the Developers have apparently been shown the door. Although one assumes a caretaker crew is still in place to keep up the servers, spawn some insane critters in the last month/week, and then turn out the lights, I don't expect they're likely to bring an entire studio back from the dead.
City Of Heroes: Freedom - the F2P version of the game appears to have been launched Sept 27th 2011; it bought the game a little more than one year more of life. In that year, about half the press releases from the company were biweekly announcements about great things you could buy with "Paragon Points": the cash to game currency conversion.
Apparently that didn't work all that well.
There are other reasons floating around - ambivalence from ArenaNET/NCSoft towards maintaining a NA Development studio when their markets/offices are increasingly elsewhere is the prevailing one - but I'm going to go with the most obvious: CoH was an 8 year old game well into the tail end of it's player base; still beloved and in people's memories but no longer played nor paid for by many of those that flocked to it initially. Not only that, but the number of comments from people hoping they port the Character Generator to it's own engine and release that separately as a stand alone going away present still makes me wonder how many people were playing the game, and how many were simply playing Super-Hero Designer inside one of the best tools for doing it currently on the market by all accounts.
So, what we learn from this is that F2P has the potential to get people in the door and interested again but you need to be able to sustain that burst and get them to buy your perks in order for it to actually prevent your product from failing. Newer games may have greater success at that because they are the "new shiny", but they too can potentially run into problems over the long term because their continued existence is now reliant on keeping those free players entertained and shopping or enthralled enough to buy into the premium product.
Which raises the question: why do we even call this F2P? Because of the illusion that the game is now "free"? It would be easy to come up with some derogatory term for what this model actually is but that would only serve to get people combative so I'm going to skip that and just close with the following: the reality is that the game is only free to play to those that are not paying. Someone else is still paying the bills even if you are not and when there's no longer enough people willing to pay for you to be able to play, your game is still going to die.
Do enjoy the ride in the meantime though.