User blog comment:B214/Question and Answers 6/@comment-185.112.105.215-20170126173810/@comment-9595671-20170127012720

Maybe he's considered as both his King & his Queen for his team, so his team's already been maxed out. While other gods may not have this same rule, the Hindu pantheon being the strongest means they have this additional rule slapped onto them for fairness.

If we recall some of Issei's power ups seemed to get banned in Rating Games after he uses them, it's possible that Gods in the Azazel Cup are limited to just martial arts and maybe their weapons depending on what they are to even the playing field more.