Who's paying these ransomware threats? I'm not aware of any psychological studies (i.e. who's most at risk), but as noted in the story, at least one police department, and no doubt anyone else who doesn't mind coughing up $200 or whatever it costs to make the problem go away are likely payers.
Like a lot of scams, criminals use a shotgun approach, and hit as many people as possible -- young, old, and everywhere in between. If even a fraction of these victims pay, then the attackers hit payday.
Of course, ransomware has that added wrinkle that people's personal data -- photos, emails, documents -- might get deleted, unless they pay. In addition, PowerLocker's creator touted the ability to lock the PC, disabling the Windows Task manager, the use of control-alt-delete, or any attempt to hid the ransom screen. Simply being able to use their PC again would likely scare a lot of people into paying up.