If the head of a trading company can make money, why he hires more traders and trains them for trading? Why he cannot trading millions of dollars himself, instead spread the money to many traders?
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. Also a single person can only handle a very small number of different markets before mistakes will eat up all the profits. Additionally, they might get idiots willing to pay for the training. In that case the money is safer and easier to make than go bet in the markets.
Most prop firms out there are for people to get higher leverage than any retail broker can give and make their money in commissions. Many prop firms that make you trade their "system" and/or pay for education are not very good. I've personally signed up for a few and I know people who's spend thousands on them. 99% of the information is everything you can find on Google for yourself, such as gap trading, imbalances, etc. None of it is really proprietary unless you are talking about a firm like SMB or Jane Street with their own software, screeners, etc.. Any firm trying to sell you a "winning method" is snake oil.
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.