I want you to consider the two states of reality from before OP deposited to after OP was returned money.

Prior to deposit: No bets have been made. Balance is X.
After return: Bets have been made. Balance is X.

The fact that Sportsbet.io accepted bets means that they were willing to take the player's money in the case of a loss. Given that the player has instead won, the casino is now instead liable to pay up. Unfortunately, due to them using their arbitrary ToS, they are able to quote a clause that gives them absolute discretion and they are able to essentially nullify the player's wins.

Now imagine this.

I offer you a bet. If you win, I freeze your winnings and return your deposit. If you lose, I take your money. I cover details allowing me to arbitrarily freeze balances if I consider you a negative to my casino in a clause outlined within the ToS. You agreed to this. I can now act accordingly to everyone else who agrees to the ToS, because of course, contracts are all-encompassing and if you were too stupid to read it then you deserve to get scammed.