The GBU-57 used here is an outgrowth of the demonstrated inadequacy of traditional bunker busters bombs used in the Middle East after 9/11. They needed something more specialized for deep penetration than the old bunker busters. This was kind of a stopgap weapon that works pretty well but the size limits the practicality.

US is developing a new generation of purpose-built deep penetration bombs that are a fraction of the size of the GBU-57.