Do you not know how natural selection and evolution work?
The drive we have towards orgasm is in fact more than any other species except perhaps dolphins and that is linked also to why our species took over the planet, intelligence-aside.
Due to the sex drive and experience of humans being so pleasurable and addictive, we not only reproduced on the higher end of the spectrum vs our death rate but we had a selfish reason to be genuinely loyal and attached to the one we regularly had sex with.
The reason why we transitioned towards monogamy wasn't just logical, it was biochemical, that feeling of 'love' when you are experiencing euphoria from being in love with someone is linked inextricably to how unique you find (even potential) sex that leads to reproduction with them. This sounds extremely superficial and ridiculous at first because some fall in love long before they have sex but I am talking about potential to reproduce, not sex alone.
When someone has many traits, not just looks, that you see as something that you'd want to mix with your genes and produce a being with this is actually the core subsconsious drive that leads us to find people who appear, act, move, talk, listen etc a certain way as far sexier than others. There's no universal scale but generally speaking females who are heterosexual seek taller, mentally-stimulating men who are passionate as their intial general thing to go for (then factors that separate the long-term from the short-term come into play) and males who are heterosexual generally seek out females who are built whatever 'medium' is, who are entertained by them and appreciate them when they (the men) are very passionate about something (and again, then factors that are long-term to short-term come into play).
Obviously I just was generic, people have types that deviate from the norm. Some like very dominant bossy women who are built this way or that, some like very passive, patient men who listen and reassure well, often an extremely bad experience with a certain type can strongly lead to one's type altering slightly.
The core drive to have sex with someone though, is rooted entirely in a relentless need to feel euphoria. You will literally orgasm at the peak/hardest with someone who is truly your type and who you feel 100% appreciate by as well (though to be appreciated itself is part of the type for both genders, generally).
In the past, those who were less driven to sex had their gene pool deteriorate over time.