There are certainly a couple explanations outside of general randiness for why there are 42 condoms available for every athlete. Though the Olympic Committee isn't saying it, fears about the Zika virus are certainly one driving force. Another is that this is the first time that the IOC is distributing female condoms, which may also be driven by fears about Zika.
Even the comparatively paltry number of condoms sent to London were a heavy haul historically. The Daily Beast reports that condoms were first distributed at the 1988 Seoul Games. There, 8,500 condoms were distributed, resulting in many condoms being found on rooftops around the Olympic Village. The Olympic Association banned outdoor sex inside the Olympic Village in response.
The 1992 Barcelona Games received 90,000 condoms, a huge number compared to just 15,000 at the 1996 Atlanta Olympics. The 2000 Sydney Games had an initial order of 70,000, but organizers had to order another 20,000 because they ran out halfway through. Athens set a record in 2004 when Durex donated 130,000 condoms.