To put it plainly, you are programmed to reproduce. Let's say by "smart" we mean "in the top 5 percent of the population in terms of intelligence and education." Generally speaking, smart people seek out other smart people to hang out with, simply because they get bored otherwise.
Now quit thinking you're smarter than the 3 billion base pairs in your genome and 4 billion years of evolution. And if they're going to spend a lot of time with someone, intelligence in a partner is pretty much a requirement. Now, luckily, the world's kinda big, so the remaining 5 percent of the gender of your choice is still a plentiful 160 million or so people.
The writing of the books was precipitated by the endemic dating woes on the Harvard campus as I observed them as an advisor and, earlier, indulged in them as a student.
Those kids graduate and pretty much continue to have the same dating woes -- only now with fewer single people around who happen to live in the same building and share meals with them every day.
I wrote a whole 280-page book about that, so that's a story for a different day. You don't feel like a fully-realized sexual being and therefore don't act like one.
At some point in your life, you got pegged as a smart person.
And making someone feel a certain way is a somewhat nonlinear process that requires a different kind of mastery than that of calculus or Shakespeare.Or never bothered to cultivate your sensuality as a woman. Attracting a partner is all about the dance of polarity.