If you want my guess, I'd wager my chips on image. There's enough misinformation out there about Crypto being used for shady, illegal, back room dealings. The adult entertainment industry tries REAAAAALLY hard to keep this clean image of safety and all that fun jazz, that I think they're staying away from crypto because they don't want the negative (and incorrect) reputation attached to it.
Hopefully that changes soon!
Thank you for sharing your view!