I believe it has to do with the team skill cap level and it's incentive to build new teams once the team members improve enough. It's difficult to field a team under the cap.If ever there was a reason to abandon the arbitrary capped levels it's this. Why not just switch to FR and use 50point levels? Even that is pretty big range, but not the absolute chasm between a 560FR sl7 and a 710FR sl7.
Bigger numbers reach the cap quicker and as it is is the happy medium APA settled on.