My understanding is that the Gambino's were the first Family to realize the potential stock scams and that Lombardozzi was the point man. As time went on,all of the Five Families had guys in this lucrative income stream. The Families have always had huge rackets like the gas scams,construction bid rigging,union control,narcotics,etc. Most of these businesses are the province of Capos and above,and many are shared by several Families.
Lots of Captains and Bosses accumulate great wealth in legitimate business,which they fund with racket money that needs to be laundered.
Since Capos kick up a smaller percentage of their earnings than Soldiers do,they can get in on better "investment opportunities". Generally speaking,the longer a guy stays an Associate or Soldier,the more he lives from score to score.