Oh good grief, think about it this way. They are in a foreign country, most of them anyway, probably will never come back so they are on a once in a lifetime vacation. Toss in the fact that just making it is as good as most of them will ever get.
Of course there is rampant sex, many of them are done in the first few days to week. Nobody goes home early, they are staying for the ending celebration stuff. Some don't do anything until the last week or two anyway. With nothing to do but watch the other athletes or have sex, sex wins fast.
Toss in the simple fact they are all under a lot of stress. I wouldn't be surprised if there are orgies. Besides most are single, it takes a rather single mindedness just to get there. No country will send anything but the extreme best. Ignore the fact that most medals go to three countries, they are all competing hard for three medals in each event.
Well except swimming, I think that is just Phelps again but otherwise.