Perhaps because power corrupts, or perhaps because we promote people into managerial roles because they're excellent at their jobs, and we assume that they will pick up the people skills, pick up the management skills along the way.
Quizás porque el poder corrompe, o quizás porque se asciende a la gente a puestos directivos cuando destacan haciendo su trabajo, y asumimos que adquirirán de paso habilidades interpersonales y directivas.