A few comments.
First, some of the women are unattractive.
Second, quite a few are lesbians - not that THAT necessarily makes a difference.
Third, there HAVE been shows where the guy has a ...nevermind. I remember one in particular where the guy apologized to the woman shortly after meeting her, telling that he routinely wakes up that way.
Fourth . . . you make a good point. There was one episode where the girl actually asked the guy to keep her warm at night by lying on top of her. Now, I'll grant, the temperature was in the low 50s and hypothermia isn't particularly conducive to romance, but still! I don't think she cared, though. She was an attractive lesbian and she really did like the guy. If anything happened, she probably forgave him for it.
There have been several episodes where the man refused to cuddle with the woman at night, getting them quite upset. I agree. If it's cold and a person's life (or survival on the show since it is meant to demonstrate wilderness survival techniques) is on the line, then it's pretty stupid or mean to refuse to share body warmth at night.
I enjoy the show. And it's surprising how UNEROTIC it is. Very quickly, you forget about the nudity and just focus on how amazing it is that these people can go 21 days without much of anything at all to help them survive. Remarkable. I don't think I could do it.