I'd say I know slightly more people who didn't change their names than did, or couples where both changed their name to something different they'd chosen or a double-barrelled or hybrid name.
Thing is, even 20 or 30 years ago, particularly if you married fairly young, you would only have a handful of things to change if you changed your name - bank account (if you had one), driving license, inland revenue details, utility bills, records at work, that's about it. Now, just think of how many on line accounts, loyalty cards, store and credit cards, services, etc. plus all the ones from before. I would imagine it would be an absolute nightmare trying to make sure every single one got changed.
Also, I've heard too many stories of women who've been shafted by banks, utility providers, etc., where they've changed their surname to that of their husbands and they get arsey about talking to them without the agreement of the husband, and such.