There's definitely a fetish driving this but I'm still trying to understand the exact dynamics...
Detective hat time. I wonder if it's actually because they don't spend much time together on these holidays. Becks would never admit it, but she's out of breath just talking - I wonder how many 'naps' she takes in the hotel while he can go out and actually explore. The bit when JP walks off from her on the beach makes it seem like he's bored out of his mind and itching to do a bit more. And she at least is returning to the hotel during the day, because she went back to show off her Sephora purchases.
And surely, surely, he can't know Tattle exists. He seems like such a private person, I can't imagine he would stay with her if he knew he was being dissected on here.
I know, thinking this deeply into it is insane, but I've got some weird addiction to this orange blob and the classically handsome little JP.