Well here's is my take on it:
Marriage is a legal contract. There are legal obligations, and there are legal benefits. Because of the legal protective umbrellas that come with marriage I am 100% for everybody being allowed to get married to a person of their choice for as long as their love lasts. I believe in a supposedly "secular" country like USA, marriage is a legal contract first and foremost (religious institutional overtones are optional). If you agree with all the things that fulfill an obligation such as a marriage, and you determine the benefits would enrich your quality of life, then yes, you might want to consider marriage.
Some folks don't necessarily find that marriage would improve their quality of life, as it might hamper their social and professional lives without having a satisfactory compensation. Financial mergers, added family members, and shared living obligations, are not necessarily satisfactory compensations for a person who is already enjoying their standard of life without being married. There are plenty of those people around, and they may not find personal fulfillment from a traditional marriage and that is fine too.
I think most societies around the world do push for adults (especially women) to be paired with a mate. Many times the most acceptable way to do this is through marriage.
I am 24 and married myself. Have been for over three years, and I find it works just fine for me, but I'm sure there are many 24 y.o. women who would not find it suitable to be married. But I think just because a person isn't married right now, doesn't mean they're anti-marriage. A lot of people confuse "not meeting suitable mates" with being "anti-marriage" also.