Frank Calabrese Jr said in a few interviews that the Chicago Outfit did not allow it's members to recruit their sons and younger relatives into their organization. With that being said, obviously that rule was broken, as his Father forced him into the life (I believe James Marcello's Father was also involved in the Outfit). But it seems that the Outfit as a whole followed the rule strictly. That's going to shrink your recruitment pool big time, as the N.Y family members often brought sons into the life.

As another poster said, the Outfit was never as big membership wise as the other N.Y families (or maybe they equaled in size to the smaller ones at least). But from what I understand, they had a lot of associates, and they gave their associates more power and leeway as opposed to N.Y. The Outfit has always had a lot of powerful Non-Italian associates, because the Outfit was never structured quite like the other American Mafia families.