I think you misenderstood that part of my text. Maybe because you didn’t read it trough.
If a game has more player = it’s more fun. No arguement here, cause the product which can get the more costumer is better one. No feeling here, just business wise.
That’s it. That means, if even if you and me prefer ToS over WoW, that wont make it successful and more fun till it has as large playerbase as WoW.
You can go by that logic and understand why I said that fun is not a factor, cause it’s a personal taste and so because of that, you can’t say that:
“My game is much more expensive, because I said it’s much more enjoyable than the others!”
What makes you say so? Having fun is based on invidual person and because of that, you can say it’s not a factor.
For a harsh example, it’s just like law. Even law is determined by something, which is accepted by the most of the people. Even if it’s ok to steal your bike for some, and they say it’s ok, the most of us wont let this happen.
The game is successful and fun if it’s played and loved by many and not abandoned. Can we say that WoW is fun? Yeah, certainly cause it’s alive for more than 15y and people still playing it and paying for it. Even if it’s not fun for me, it is enjoyable to others.
Are we clear now? 
Also, this arguement is going for business model and what determines a successful game. Please do not make this topic into a “what is better game”, cause the better game is always the one which can be fun to you.