I believe you hit right on the money. It's all about ratings. I believe that's why we see the new couple Leora and Paul having so much sex. So much that I believe last night's fight was over that very issue. Sex leads to ratings, ratings let them stay in the apartments.
But of course this is why we watch so, ... the sex, right?
I suspected as much but I hope this isn't true. If it were, that may encourage the couples to specifically put on a show for us rather than live their lives regularly, which kinda defeats the purpose.
As for the sex issue, seeing as how I don't understand anything that's said between any of the couples, I am mainly interested in the sex but catching them having sex is more fun and appealing when you have a better sense of who they are and what they're going through.