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.