If the rewards will continuously decrease the players will start to pissed off and get tired on your events. Admins should pay attention on this kind of situation and should focusing on giving the players what they deserve. Yet, we should give them some time to get better and there is always a room for improvement.
I think they are becoming losers day by day for sportsbooks that's why they are decreasing rewards and promotional offer day by day as they do have not sufficient funds to spend. If my imagination is wrong then they have enough users who are using their service that's why they are ignoring the demands of their users.