The rewards are only reduced for accounts that don't do at least a little gambling, buying lottery tickets or deposit to keep a higher balance.
The bots pay for captcha solves and when we reduced the reward for those accounts last time those botnets stopped briefly and weren't buying captchas. So the sites that sell captcha solves reduced their prices so the botnets were profitable again. This latest reduction really is the only thing we can do. It is targetted at accounts that really do nothing or very little other than draining the faucet. It is a gradual reduction by a very small % per day.