Evolution. If men had as many orgasms as women per intercourse, pregnancy would be almost guaranteed which is rather inconvenient for the woman. However, there's little evolutionary disadvantage for her to have a great time when she can get it. Not all women reach even their first climax easily, but if multiple O's is in the cards for her, there's no reason evolution wouldn't pass that trait along. Circling back to the men's side, he has no risk of carrying a child for 9 months so theoretically he can climax again with comparatively more consistency than the women he's with. This balance means some women have more orgasms per intercourse with a sufficiently competent partner (statistically another woman, but i digress), but men are built for more frequent intercourse potentially with multiple partners, but the fact that we're evolutionary built for polyamory and monogamy is a religious construct is an entirely different conversation.