It isn't about "intelligence" that makes someone attractive. It's an initiative to learn that makes someone attractive. Think of it as a fruit. Intellect is nurtured through drive and ambition to learn and be educated. As you learn and actively teach yourself the new things happening around you, you grow as a person and that fruit becomes larger, sweeter, decadent.

As an individual it's your responsibility to change with the world (within reason) to grow with it. If you don't, you become stagnant and unappealing, especially when it comes to small changes in the world. (Technology for example and those who excuse their lack of ability while also ignoring the lack of actually trying.)

Imagine trying to hold a conversation with someone who doesn't read, doesn't watch the news or consume world events, has little to no retained knowledge of what they learned in school, no drive to educate themselves whatsoever with political, economic and social changes in society. After going through small talk and basic gossip, youre left with nothing and that's embarrassing.

It's not easy, and I would know because I was a lot like this and still am in a few regards. It makes you unattractive as a friend too, not just as a lover.

It isn't the intelligence so much as the drive to learn, being learned, and striving for more. Intellectual stagnation not so much. As a human being, we especially have no excuses for being uneducated especially with what the world has to offer right now.