Larger pattern of gender differences?

Of the men and women who have traveled to Japan for a summer, there is a striking difference in "availability." I choose that word because I often hear the ladies discussing their desire to "hook up" with a fella during this summer, whether a native Japanese male, or more often someone who is also a foreigner, especially when we are together in a large group. During orientation we all spent a lot of time together but there was very, very little "hooking up" and it was not for a lack of interest by the ladies. In two weeks we will all be gathering again to wrap things up.

Of the women, almost all are single. Of the few who are not single, the majority of them are married.
Of the men, almost all are in relationships, almost none of which are married.

It made me wonder... what is the cause for this. Is it pure coincidence, or something else?