Bookie can give gamblers big limits and make a business out of their addiction, when you win few bets they are limit you.
And that is fair to you, and that is morally.
This has nothing to do with morality, it is a matter of businesses being able to not service a customer if they think it is a loss for them to do it, now if you are a profitable sport bettor then good for you as you are probably better on that aspect than the majority of the gamblers on the forum, however I am pretty sure all casinos specify that their games are not for professional but for recreational gamblers, and since you are clearly not a recreational gambler then they can refuse to accept your bets.