Why was this the case? I thought they were at least as intelligent as modern humans and had more muscle mass, used rudimentary tools and had control over fire.

Why was this the case? I thought they were at least as intelligent as modern humans and had more muscle mass, used rudimentary tools and had control over fire. They lived in a climate without a lot of dangerous animals or a lot of disease and disease vectors at least compared to the jungles of Africa.