How did you reach the conclusion that they’re “heavily correlated”? From the studies you posted, I’m seeing effect sizes of r ≈ 0.2, which is usually considered a weak correlation. A change in one variable explains only about 4% of variance in the other.
An effect of this magnitude is, I suspect, consistent with left wing beliefs/ideology being transmitted at universities, whose population has already passed a selection filter on intelligence.
I just mean that Pr(left wing|went to uni) > Pr(left wing|didn’t). No assumptions about the mechanism, just observing the regularity.