So asks Eugene Volokh. His commentators adduce a number of reasons involving children, or a desire to change an ugly last name.
The cynical economist looks for signaling explanations for why the practice persists. By taking a man’s last name — a costly move — a woman signals her long-term commitment to the relationship. The real question is why the man does not take the last name of the woman. Yes this is disruptive of the man’s career but that is precisely the point. And don’t more men wreck marriages than do women, thereby implying they require more constraint?
Some men do take their wives’ last names, and more choose a hyphenated version of the two names. But do they not signal weakness in a bargaining game? (Do you see any professional wrestlers named Smythe-Thomson?) Could signaling strength in bargaining games be worth more to men than to women?