I am surprised none of you marketing wizards have ever heard of a loss leader: https://en.wikipedia.org/wiki/Loss_leader. That is more, or less, exactly what F2P and preferred players are. They increase traffic, which is what "everyone" is complaining about being missing in this game, besides content.
Comments like just merge all servers into one and only let us subs play, would surely not lead to higher sub rates. I assume the original introduction of F2P was in response to avoiding just such a situation. In other words, it is likely that if it was not for F2P, or preferred, players, your sub price would be much higher. And, probably high enough to have discouraged enough people to stop subbing that the servers would have been shut down long ago.