Shock finding: nuclear "bunker busters" dangerous

Like this isn't obvious to damn near everyone on the planet with an IQ over 70:

Nuclear “bunker busters” could destroy enemy hideouts hundreds of metres underground but, if the target is in an urban area, a strike could lead to more than a million civilian deaths, warns a report from the US National Research Council (NRC) issued on Wednesday.

"Using an earth-penetrating weapon to destroy a target 250 meters deep - the typical depth for most underground facilities - potentially could kill a devastatingly large number of people," said John Ahearne, chair of the report committee.

Why would a target for a nuclear "bunker buster" be located under a large number of human shields, err, people?