According to the FBI, most of the criminals who pull this particular stunt are professionals; this is what they do for a living, and they typically go after thousands of victims a day; if they can get just 5% to fall for it they can make a lot of money. Some of the time they actually already have a pic or two because they've been hacking webcams, and they often hang out on gaming sites where they can record dialog to use that sounds "right" to US teens. Beyond that, they are usually adults; kids who try it usually are not smart enough to keep quiet about it, and they get caught quickly.
American teens in particular are vulnerable to blackmail because of our strict child pornography laws; it's easy to convince a kid that photos they took of themselves can get them sent away forever for possessing kiddie porn. (Which is not to say that the laws are bad, they are not. It's just that teens are so scared of being tarred with that particular brush that extortionists find it easy to take advantage of that fear.)
BTW, FWIW, every mounted device webcam in our house has a basic manual slider cover on it; I buy them by the box. Most people put their phones down flat, so a hacker will get a great pic of the ceiling, but upright cams in a bedroom can be a goldmine if hacked; they can give you a view of all sorts of things. A manual slider costs pennies, and the best hacker in the world can't defeat it.