There are many examples of good engineers that are also good leaders. I think the Venn overlap isn't that unusual, at least for a good engineer leading a team up to maybe a dozen. When a good engineer lands in a spot where they get to work on something they really care about, that doesn't hurt either!
Now, how many good engineers are also good at leading larger teams? As the team size increases, my impression is that it is less common. If so, why? Lots to explore around individual, cultural, and corporate factors.
* If one sets a prior probability to 0 or 1, a posterior probability will not change due to Bayes' Rule. This means new information has no effect. Put another way, choosing either 0 or 1 as a prior is equivalent to stating "no new information will change my belief."