Not sure if you've been grading Pokemon, but if so and they're primarily in English, that may be why. I just got back a 60 card submission that was a mix of ENG and JPN cards. Across the board, the JPN cards scored much higher, including a Yu Nagaba Pikachu which came back as my only 10. The quality control on ENG cards is complete garbage in comparison, so it doesn't matter much if they're pack fresh. They're always going to be off-center with raggedy edges straight out the pack. If CGC's grading scale is taking into account the relatively higher level of quality in JPN cards, that may be why it's nearly impossible to get a 10 on an ENG card. Just something to consider.