Why put all that time and energy to get naked photos of women just to extort them not for money or sex, but for more photos? Is the Internet running out of porn? This seems like a high risk low reward crime.
It is, of course, a power thing. Yes, there's an endless supply of porn, but the "real thing," especially if gathered without consent or explicitly agains their will, is "more satisfying." To be clear, not advocating for this.