Why is there such an emphasis on couples hanging out together?

In television and movies I see a huge emphasis on couples hanging out with other couples. This is also something I see a fair amount in real life. If it’s a large group of people and there are a few couples, there doesn’t seem to be a problem, but I’ve noticed that my couple friends often want to hang out with other couples. Why is this? My boyfriend and I almost never hang out with other couples exclusively and if we do, it’s not because we want to hang out with two people who are in a romantic relationship. It’s because we want to hang out with two of our friends who happen to be going out with each other.

Perhaps the collective can shed some light on this practice.