Gian, the fact that you don't understand such an idea is very good...it speaks volumes about your character and integrity.
An honest, trustworthy person endorses a product ONLY when they believe in it AND use it. The importance of that concept is heightened to the highest degree when the endorser is also the creator of said product. Imagine someone creating a trading system/method/product, asking 'customers' to pay good money for it, but not willing to bet one dime of their own money on that product themselves in real trading. If one has devised a 'successful' method for extracting consistant profits from the markets, there is no logic whatsoever in the creator NOT using that method for their own financial benefit, year-in and year-out, retired or not. Unfortunately, this industry is rife with failed traders who resort to flogging their questionable wares to the general public when they can't make the grade on their own...sad, but true. But, whether through desperation or weak moral character, it still doesn't justify the behavior of such con-artists. Again, glad to see that you are one of the honest few. Best regards.