Why is this the way it is? iin?

Yeah, it's definitely no longer oppressive or sexist. It's just the default and usually nobody is too worried about it. If either person wants to keep their name or do something different, they can.

It's more for tradition anymore, especially in religious marriages.

it actually did not start out as a woman taking her husband's name. People actually had clan names rather than surnames. Although all women would reject it, they were actually owned by men. The phrase "the father giving away his daughter" and the tradition in weddings where the father gives his daughter's hand to her new husband and then shakes the husband's hand to conclude the "sale".
A daughter's hand in marriage was actually bought by paying in either land or gold.
To get back to my original topic, clan names. The woman usually joined the clan instead of the other way around. So she took the name of the clan. Later, as people started drifting apart and stopped living in clans, a bit of the tradition was kept. The clan would now consist of one. A man. If a woman joined the man in holy matrimony, she joined his clan. And they have tons of sex. Tons.
But I am drifting off topic now. I am so lonely.

Well think about it doesn't really matter for me a new name is a new family don't you think alfie?

It's just tradition, many women now choose to keep their last names, but some woman love the idea of changing their last name (:

What happens when the next generation of everyone giving their children hyphenated names? Then they'll have to hyphenate four names. Then we'll need to have ID cards that are five feet long.

Because the man has the cock