What makes people to stay with TB so much is other people.
You meet someone, than play with him for quite some time, than you transfer to forum and meet even more guys... It's a social part of the game and forum that makes people to stay.
Idk, how it will work with Steam, that has it's social part already. We will see.
What I don't understand is ''Nabi is giving 800 etc for nothing'', there is no busyness that will give you something for nothing, otherwise Nabi would be closed long time ago. There must be some material value in TB, and, I'm afraid, that value dropped in past few years.