Diversification is to limit risk. Having 100 people making small and different bets is safer than a single person putting all his money on one bet.
Most prop firms out there are for people to get higher leverage than any retail broker can give and make their money in commissions.
Nearly half of what you'd pay per ticket goes to the firm. Profit sharing arrangements go to the firm. At a shop where I worked, newly hired traders would share almost 70% of their profits to the firm in the forms of risk management and actual profit shared (30 % of profits shared and 40 % reserved for risk management). Plus you wouldn't get any accumulated risk management cushion if you leave the shop.
Sounds like a good deal if you don't have to put in your own money.
Did you work there as a trader or as a regular employee.