This is similar to not counting bank deposits as revenue and withdrawals as costs. Only when your money goes to pay fees is it booked as bank revenue. The same for money transmitters like Western Union.

And perhaps is more obvious when you consider what happens when there’s only players, eg, poker. The pot is held in trust, until the game ends and the losers forfeit their money to the winner. At no point does it belong to the casino.

That doesn’t change when the casino is also a player.