Even if a man only values women for sex, it's not like the majority of men have the luxury of having (frequent enough) sex outside of entering relationships. So they likely value relationships as that is their only avenue towards frequent sex where a direct money transaction isn't involved.

Also, its possible that some of the men who appear to only value women for sex do so not because they're misogynistic, but because they think they realistically can't expect to get anything beyond sex (in a relationship) from women anyway.

Due to modern cultural conditioning, many if not most women view doing most of the things beyond sex, the other things that a man values in a relationship as "oppression", and his desire for those things as "misogyny". And whether or not men are bold enough to admit this, most of us are somewhat aware of this.

What we see nowadays is that they often only offer more than sex for a man in a relationship when they find him extremely attractive,

my personal experience with that being one GF who thought I'm super handsome would cook often, not place many demands on me, be receptive to things I want to do (not just HER HER HER all the time) etc.. another GF that didn't find me all that attractive was the opposite, and I can confidently say sex was mainly all I got out of that relationship, despite wanting more.