I apparently missed some attempted explanations of Carnival on the Logos blog for Logos software.
Folks, Lent and Advent are penitential periods. At many times during Church history, couples were instructed to pray together at night instead of getting nuptial. And thus, no nuptials, either. Advent and Lent marriages imply that you’re not getting any or that you are determined not to be penitent, which is why Father doesn’t want anybody at the parish asking for such a thing. (Especially since it would really put a dent in the proper celebration of your wedding feast.)
Carnival was the time for fun, and for getting married in a hurry before Lent starts — if you were too scared to get married back in the summer, like a sane person.
June marriages not only went along with Roman and Jewish custom, but also conveniently were well before Lent and Advent.