Same in the UK. In straight marriages, the woman does often change her name, but it’s not automatic. Actually, I’m surprised at how many young women I know who’ve changed their name on marriage.
With lesbian couples I know who have civil partnerships, some have made themselves a double-barreled name, some have kept their original names, and some have taken on one partners’ name for both. Two couples I know made up a completely new name. I only know a couple of gay male couples who have CPs, and they’ve kept their own names.