As a kid, at some age I realized that when people tell me "you are smart", it means that I said something they agree with. They certainly didn't reward a clever argument again their ideas. (Another source of praise was when I won some mathematical competition, because that was socially neutral; a pure signal of skills, evaluated by some external expert.)
I've actually had people call me smart for arguing against them quite often. It's a kind of defense mechanism - 'you're only winning the argument because you're smart, not because you're right'.
One of the big variations I see between people is the amount of energy they habitually put into thinking, and I haven't seen this discussed anywhere.
General advice about improving health and lowering intellectual friction would seem to help increase the ability to think, and ideas like "take five minutes to consider the problem" adds impetus, but I'm not sure what the general difference is between me and most people, or Yvain and me.
Intellectual drive isn't an unalloyed good-- cranks have high drive combined with low self-editinig, and some types of depression include a compulsion to think about topics that cause misery and/or inertia. Part (all?) of the value of meditation is getting some time off from thinking. Still, increasing intellectual drive would probably be a good thing for a lot of people.
Has anyone found that rationality training or anything else increases the default desire to think?