Were you running supersim from within a game?
Changing the quarter length from Settings makes no difference to the season wide number of plays which are generated when running an entire season.
I just ran another test (using SABO's latest mod v1.1) - the number of plays (pass attempts, rush attempts & sacks) added up to 30,125 plays.
That works out at 941 a team or 58.8 a game. This is 4 plays a game too low.
AFAIK the only way to fix this is via Frosty. Or the devs of course.