Marriage was designed as a patriarchial institution, in which women were owned and controlled by men. It wasnt that long ago, that a married woman was legally owned in the UK, by her Husband. And many of the customs of a wedding reflect that status.
So it makes sense to critique marriage from a feminist perspective. I think marriage has changed, certainly legally. But it is still used as a cultural prop to control and subordinate women.
Look at the emphasis on the wedding day being the best day of your life. And the emphasis on making your marriage work, and the subsequent shame many women feel if they end up divorcing.
I think making your marriage work is BS. If you have chosen the right person, then yes there will be conflicts that you have to deal with as in any relationship. But the working at it trope, keeps a lot of women in bad marriages.
Also in society women who are married do have higher social status than women who are not. That is a reality, and that makes marriage very attractive for many women.
So given that context, being proud to be married, or being proud to have a long happy marriage, is open to feminist critique.