Because we're intersubjective beings. Difference in intelligence level alienates one from the other. Past two standard deviations, anything like a "meeting of minds" becomes impossible. The only mutual interactions past that delta are economic ones (money exchanged for goods/services).

Hegel declared the Cartesian cognito can't exist in the singular. Lacan, Deleuze, Husserl, and many others said the same, that the subject is a function of its dialectic with the other. Dasein is Mitsein. There is no complete subject, floating in space by himself. Without an other, the subject cannot exist, at best becoming an object, at worst psychotic. Either way, isolation is a process towards annihilation.

If you're smart, find other smart people for authentic interaction. Likewise if you're not smart, though the problem there is easier for statistical reasons. Find them, turn off your parasocial pacifiers, and talk. You'll know it when you've found someone compatible, because you'll be able to emulate their mind, and they yours. It's not just a nice to have, but a need, a necessary component for survival. Without it, the sane you will cease to be, replaced by a zombie or a madman.