Lack of intelligence isn’t the issue. Take the dumbest person you know and imagine they’re trapped in a room with no visible escape path. They panic and start destroying whatever’s in the room. They damage themselves in a fit trying to escape. Now take that same scenario but put in small creature comforts and distractions. Now your dumb friend isn’t panicking or fighting to get out. He’s still trapped and his intelligence neither helped or harmed his situation. This is what’s happened over the last 100 years, and it’s accelerated to decline.