One of my old roommates and I had many conversations about this: When you're single and in your late twenties, you don't want to have to wait some indeterminate amount of time until you get married to have decent plates or towels that match or a non-twin size bed, or whatever.
It's not necessarily that we want to project the image of being that utterly independent, home-owning, job-loving career woman who doesn't need anyone, but I think that's the vibe people often get when women choose not to wait until they're married to quit living like college students.
Keep throwing money away on rent, eat off mismatched plates, settle for hand-me-downs, work crap part-time jobs, and wait for the right man to come along? Or buy a house and your own dishes, find a good career, and give everyone the impression that you're a Lone Ranger and don't want a man at all?
*Based on thoughts and comments AGES ago on the lovely Fiona's blog.