The grander the scale, the greater the reward. Therefore, the selling of investment advice and investment-management services is no different than the selling of toilet paper or Tide. Economy of scale and a remunerative payment structure are key. If an investment advisor can cobble together 50,000 subscribers willing to pay $50 each annually for his advice, he'll be a millionaire in short time. If an investment manager can cobble together a few billion dollars and collect 2% of funds under management and 20% of anything above the 6%-return threshold, he'll be a millionaire in short time (very short time in a bull market).
The investment advisor and the investment manager may very well be remarkable traders of public securities and create value for their customers (I'm not implying anything is inherently deceptive or fraudulent about theses businesses), but even if they're not, they'll still accumulate a decent fortune if they can hang in there long enough -- but that's the case for any business person.