For some reason I just picture Cardassians having a hard time with the concept of "casual and brief." When they go into a relationship, from what I've observed, it seems to be very serious. So, personally I just figured Dakal would rather be single than go into a fling that he knew wasn't going to be permanent.
I'm not so sure shipboard romance HAS to be a fling, though--but it takes two very committed parties, and I'm not sure how many of the cultures there, besides Cardassians (and I'm not even really counting humanity) accept that concept anymore.
But then I'm old-fashioned. I like marriage stories, seeing people in it for the long haul and really putting the work into the relationship to make it last. (Which is one reason I like Riker/Troi.) Maybe that's one reason I identify with Cardassians--they seem to look at things the same way. (Dukat doesn't count. That man was SICK.)