It's not that we want clingyness, it is that we may prefer that course of action because it proves you actually care and puts half of our doubts to rest. It is insecurity on our part. If we cannot see you care, we are left to speculate you really don't and have an alternative motive. And the reasoning we don't reciprocate is rather obvious. We are us.What's funny about INTP guys is that they want you to be clingy (if you weren't they'd flip out). But they will never reciprocate the kind of behavior they expect from you.
In some ways, it seems sexist, at times.