Now imagine. Olympic Village. Professional athletes, that is, all of reproductive age (~ 17 to ~ 35 years old). All, I assure you, all polls are charged with exogenous hormones (sex hormones, of course), i.e. doping, head over heels. There are no hard workouts, there are only "leads" to the starts. Getting out, taking a walk around the city, before the start, is unlikely to be so easy, because the regime and the Olympian are too valuable a frame to just let him go for a walk in a foreign country. Well, it's clear how they start to have fun. I read somewhere that hellish sodomy is happening in the Olympic villages =) As a result, protection against the spread of various diseases, as already answered.
In order to avoid the spread of viral infections and diseases, obviously.
Most of the Olympiad participants have a lot of free time, and there is no wife / husband or children nearby. Sex has always been the best pastime and relaxation. Since 1992, it seems, the distribution of contraceptives has been organized in order to secure the spread, first of all, of AIDS. Today, the spreading Zika virus is a problem in Brazil - and all those 450 thousand condoms (350 thousand for men and 100 thousand for women, respectively) will be covered with some kind of lubricant that protects against the spread of the virus.
In the end, the Olympic Committee decided that it was better to prevent the consequences than to prohibit sex, because no one listens to the prohibition.