Well subscriptions allow some profit to come in, but most of it is used for keeping the servers going. The F2P model appeals to kids who are either too cheap and lazy to fork 20 bucks on a game, or people who can some how afford a nice computer, but not a game. So you have that item market whcuch sells skins and stuff which keeps the game going. Also with advertising the company that runs the game gets paid for each person that gets bombed with adds. So lots of cheapskates + ads = money = game living.