Are marriages outdated?

They have four children, 2 dogs and 7 years together and seem reasonably happy. She is the only unmarried one out of her tight quartet of friends but ironically also the one with the least amount of drama, infidelity and fighting in their relationship. Her friends and family keep asking her when her significant other is going to put a ring on it but Marcia* always smile and shrugged off the suggestion that she needs to tie the knot. For her things are perfectly fine the way they are.