Can someone explain this to me? The article says: "People who carry a harmful genetic variant die at a higher rate, so the variant becomes rarer in the older po

Can someone explain this to me? The article says: "People who carry a harmful genetic variant die at a higher rate, so the variant becomes rarer in the older portion of the population." However, this is the opposite of how I understand evolution: "harmful" variants (from the evolutionary point of view) should become rarer in the younger portion of the population- whatever happens to their original carriers is irrelevant. Also "researchers scoured large US and UK genetic databases"- well, I wouldn't be too sure that the biggest part of evolution happening in the human species can be seen inside the UK and US genetic databases.