Maybe SH requiring all CH to rate every entry?? To provide each creative an idea of improving submissions on following contests.
One thing that may encourage CHs to rate entries is by an assurance of 10-20 dollar cashback after rating everything. A cashback that may be included on the initial CH’s payment.
Rating entries must also have a specific deadline. Like maybe three (3) weeks after the end of the contest so creatives still have chance to check and report on (sometimes) ‘stolen’ domains
If a CH hasn’t rated any submissions in around 5 days, it would be helpful if they could get a gentle NUDGE from SH.
It’s very frustrating for Creatives who have put in a ton of time and effort, to not get any type of feedback from Clients for days, and in some cases, no feedback at all, and the project closes with ZERO ratings. 
Also, it’s very counter-productive for CH’s not to rate any entries. I don’t enter a lot of contests but when I do, I initially submit a maximum of 3 entries. If I receive ratings (even NTY ones) then I will enter more. If I don’t receive any ratings, I just move on. Without ratings I have absolutely no direction to go on. I don’t want to keep firing off entries into some sort of void which likely cause my overall % to go down. It’s definitely a losing proposition all around for a CH not to rate entries.
Five to seven days maximum