This scam is successful because it is predicated on the same appeal that ventures like lotteries, sweepstakes, slot machines, or giveaways have (albeit accentuated with a seemingly guaranteed win, that these other ventures don't have): the belief that you can just luck into a giant treasure chest of money by expanding minimal effort.
Broadly, this is a modern version of what's known as an advance-fee fraud, which has been around for hundreds of years - paying a small amount upfront (hence the 'advance fee') under pretense of receiving a much larger amount later.
Broadly, this is a modern version of what's known as an advance-fee fraud, which has been around for hundreds of years - paying a small amount upfront (hence the 'advance fee') under pretense of receiving a much larger amount later.