Why do atheists rely on blanket statements like saying nonatheists don't care about making the world better

It seems like they just overgeneralize based on the fake religious people that get talked about in the media like ann coultry and pat robertson, rather than from a real understanding of religion. But it's rather convenient that they never mention the people like Martin Luther KIng or Gandhi. Because since when has an atheist done more in terms of major social progress than say Martin Luther KIng or Gandhi to be talking like that?