That's kind of an odd-ball statement that implies that the only people that watch these sailing blogs are dirty old men that have a need to see girls in bikinis on sailboats. From my perspective, nothing could be further from the reality. I'd say it's a combination of the destinations and the relationships. I think it's true that couples, or multiples of relationships (such as Delos) are what attracts viewers. I typically seek out the blogs where I might relate to the destinations. Sue gets fully involved in the relationships. Sue is far from an avid sailor, and she doesn't have any particular need to watch sailing blogs, but there are a few that she is totally vested in watching every episode because she has developed a strong attachment to the couples, as if they are personal friends. She has a personal interest in where they go, what they video record, everything personal that they go through. She keeps up with them on social media and she wants to make contributions to their adventures, probably because these people have opened a window into their lives (and their lives are interesting) in a very personal way. It's as if they are close friends. It's reality television in it's best form.
I think it is simply archaic thinking to suggest that it is all about "sex sells". Maybe for lonely men, but there is so much out there that is new and evolving with these sailing blogs. The relationships that they create with their audience goes way beyond that, I think in a good way!