Jezebel just posted Samhita Mukhopadhyay's "Ten Very Good Reasons You Aren’t Married Yet." The reasons that make sense are about why you're not in a relationship; the ones that don't presume a happy romantic relationship between two adults who could legally marry but are choosing not to do so. The latter are good pretexts for why you're not marrying someone it seems you ought to be marrying, if you think you could do better but aren't sure and are biding your time, or who knows.
One by one...
1. Yes, if you put your career first, and must be able to move halfway across the world at the drop of a hat, and do not have a waking moment to focus on the concerns of anyone but your employer, you should probably be single. But what you don't want to do is gratuitously perpetuate the stereotype that women (never men, just women) who are married have by definition dropped out of the career-not-just-a-job workforce. Married women who are also pursuing a career have to deal with enough grief about this as it is.
In fact, the idea of a wedding dress makes you break out into hives and you don't want a blood diamond, you think forever is bullshit and you have no interest in feeding into the romantic industrial complex. You have a hard time reconciling your politics with what you see as a deeply problematic institution. (Or, you're just an atheist.)