Being dumb makes you less fixated on the global issues and brings you down to a more personal level. Humanity is facing massive global issues and not having to worry about this gives you less depression, less chance for cancer etc. Also you feel less frustrated by your job if you just mindlessly, without any intentions to learn or personally grow, do your job and go home to eat fast food and relax. Being smart and trying to improve things is frustrating in a world ruled by the dumb majority. Being dumb is an evolutionary advantage now.