Back in the medieval ages when a woman was married to a man, they were basically considered property for my understanding and treated like an extension of the man’s person and family. So it was customary for women to take the man’s last name since they were being joined to his family. But now here in the 21st century women are fully independent and last names don’t really seem to mean much of anything. I mean what is Smith or McGregor or any last name really mean anymore? Especially in the digital age, lots of people have digital usernames like SarahSmith1727373. So the last name clearly doesn’t mean much anymore… Which leads me to wonder, why do the majority of women still take the man’s last name? Especially when some of them have a horrible last name? I have seen some butt ass ugly last names recently, like Fink, Weimer, Slotsky/Slotsky, Hiscock (no joke this is a last name), Hardman… And then you hear the woman’s name and it’s like something way more reasonable and less stupid sounding like Kingman, or Harrison, Walls, etc.
To all the people here arguing that it’s easier to have a family name, especially with children: It’s also possible that the husband takes the wife’s name. But from anecdotal evidence in my acquaintance, most men are very opposed to this idea. So if the woman wants a family name she has to change her name or have endless fights about it. That’s why most women I know did it.
Having one name is easier for social reasons. Going with the man’s name is easier for social reasons.
It all comes down to social pressure to keep the status quo. I even offered to take my wife’s last name and she declined and took mine instead.
Having one name (at least in common, using hyphenation) is easier for legal reasons too. If you have kids, and one parent doesn’t share a last name with them, you’ll have headaches at school, maybe crossing a border, unless you brought some extra legal documents with, etc.
In Sweden, a couple can choos to have a new last name not related to either.
You can choose another last name when you get married in the US too, but people just don’t choose to for the most part. The marriage license name change is a shortcut to a regular name change that can be made through the courts.