Also, you don't need to actually have or even know BTC to fall for this. If someone receives a email saying that will release stuff about them if he doesn't send $300 in BTC to them, they will just google what is BTC and maybe even buy it just to pay the scammer. If you believe in the email of course.
See: Indian FBI contacts senior citizens for failure to pay taxes on behalf of the IRS, but they can either repay it with Google Play Store gift cards or go to jail.
Unfortunately, scams are so common because they work on so many people. It doesn't matter if 99.99% of the population won't fall for it: the remaining percentage will line the pockets of scammers.