they dont think they want or need kids because they are young and it seems like they will live forever. But one day they wake up and realize... oh crap.. I am getting old... and who is going to take care of me when I get even worse off? surely none of these dogs I am dating! oh crap! maybe I should have kids! oh wait... I am now too old!
They know about biological time clocks. With all the Bill Clintons out there why bother thinking about it. Too much fun to ben had.