Assuming they really are (which as the sibling commenter points out, is open to question): Because it's an intrinsically high-stress role, by any metric. And

Assuming they really are (which as the sibling commenter points out, is open to question): Because it's an intrinsically high-stress role, by any metric. And on top of that, you have massive psychological expectations to answer to. Including and most especially the most toxic of all: having to shape our lives according to what other people think.