Because women have evolved to find random sex with non-superstar partners repellant, not attractive.
While you may not want kids each time you have sex, and in fact, probably don't, what appeals to you IS based on evolutionary history. For most of our evolution, for males, any random sexual encounter was pretty much a plus. A 'relationship' (i. e. bonding with a female) is something you'd be more careful about, that had benefits, but you could only really raise one family at a time, so you needed to choose carefully. But any opportunity to have sex beyond that was a plus as it might spread your genes.
On the other hand, for women, random sex is a terrible strategy. They can't spread there genes, they HAVE to be selective since they can only have one child every year or two. If the male is not going to help as a father, his genes would need to be superlative for it to be worthwhile.
Now nobody is thinking that, but it's why still today, women don't just want to randomly hookup and maybe have a relationship, while most men would view that as 'at least we had sex', most women would view that as a 'gross' mistake.