It's pretty simple:
Unmarried people get all antsy if they have to attend a segregated function.
Happily married people could care less and just enjoy the food and whatever company they have.
:D
I've been to a few gatherings, the dudes are downstairs in the basement and girls upstairs. Since every one there had a kid, guys were still coming and going... it wasn't a big deal....
as long as the people are fun to be around and the food will be good, it doesnt matter.