As I've written about before, people tend to write horror about what they fear most.
For much of his life, Lovecraft was fixated on the concepts of decline and decadence.
— Wikipedia
A lot of Lovecraft's original stories (as opposed to those from the wider Mythos) center around fears of corruption, and to corrupt an intellect it would first need to be pure, brilliant and intellectually strong to show the greatest contrast.
This is in line with Lovecraft's fear of society as a whole being corrupted by non-white people, which are rooted in his racism.
I cannot think of a non-white character in all of his stories that undergoes this intellectual corrupting transition, they're all shown as already degenerate.
Separately, he's a believer in Cosmiscism, and the advent of quantum physics and 'spooky action at a distance' would have definitely led him to look for excuses to discuss those concepts in his stories.
Now all my tales are based on the fundamental premise that common human laws and interests and emotions have no validity or significance in the vast cosmos-at-large. [...]
— H. P. Lovecraft, in note to the editor of Weird Tales, on resubmission of "The Call of Cthulhu"
By and large you have the right idea, that only the brightest could be corrupted, but it's not only thing going on with Lovecraft's stories.