I am asking myself: Are all of those credits from active user accounts? As kingnight2 said he didn't even knew he had credits to spent on trainer requests.
Even though it might lead to more work for you CH guys but would a reminder email from time to time be anything to think about?
If the amount of unspent credits is taken into account of how much credits have to be spent on requests it inevitably leads to higher numbers.
Ever thought of using the "Transfer" option for your unused request points to another user? Maybe someone whose posting you liked on the forums or who shared rare cheats or whatever reason?
[Edited by Taurusplopp, 3/26/2016 6:25:46 PM]