Because they can do both. They can trade their own account and get an allocation with a % split. If you are at the same broker, they can set up post trade allocation to trade multiple accounts pari passu.
I am sure they can, even trade 6 accounts at the same time!
Some people are VG at trading other peoples money, for the simple reason that there are no emotional attachments, so if they lose, they don't really care.
Can one make money giving control of your finances to someone else, heck yes, lots of money, but it can easily go the other way as well.
No reward without risk, no matter what any person may try to tell you, or, sell you!
Trading is a mugs game, but only if you are a mug!
Open you eyes (mind), get off your fat lazy arse, work out the odds, and play the game. You can make money once you keep in the game, which I should not have to mention how accomplished.
100 pennies make a pound, or again for our young know alls, 100 cents make a dollar!
J_S