As an example, if anybody tells you their commute to work is 25 minutes, it's more likely 45 minutes. "It takes me 10 minutes to get to X" really means 20. I don't know what it is but people just don't get this right.
It's way worse when it comes to money. "My income is $X" literally means "My income is 0.3X to 0.7X". I need to see employment contracts and W2s before I believe you what you say about your salary. People will even lie anonymously (eg on surveys). It's like they need to believe it themselves.
So when you say you have friends who net win hundreds of dollars, unless you've seen P&Ls, I don't believe them. And I'm sure these sites don't make it easy to figure out your total P&L because then you might stop. People will remember and boast about their wins and downplay or just plain forget their losses. They'll minimize losses and exaggerate wins. It's just human nature.
Ever notice how no gambler says they consistently lose? Everyone is somehow a winner? Isn't that sus?
That's just not true. Fanduel for example shows your lifetime win/loss statement ("career stats") prominently on your account page, including your Net Total in a large number right on top that is impossible to miss or ignore.
Most people lose, because you are paying a vig, so you have to win ~60% of your bets just to break even, but that doesn't mean everyone loses - they certainly don't. This is evidenced by the fact that people who routinely win from the sportsbooks can and do get banned.
This is only true in some cases and entirely depends on your form of gambling. Draftkings and Fanduel both run "daily fantasy" and sportbooks, and they are quite different. If you win consistently enough on the sportsbook, then you are taking money from the house, and they will ban you. The "daily fantasy" gambling on the other hand, works on a paramutual basis where they take their profits off the top. For example they will take 20% of the total prize pool regardless of who ends up winning or losing. Much like the track when it comes to horse racing, they don't care who wins or loses because they are getting the same % either way, and the more volume there is the more money they make.