If I give you 1 BTC and tell you that you have to wager 10 BTC at a 10% house edge, the EV of that bonus is exactly 0, as you calculate above.
I think there's an idea is when you "bust" your bonus, it's over. You can never lose. Your worst case is making 0 btc profit, but you can make money from the bonus, ergo the EV needs to be >0