Unlike the 1984 Sarajevo Olympic venues, which were destroyed during the Bosnian War, there was no catastrophic event that led to the abandonment of the Athens arenas.
Greece simply has no use for world-class, expensive-to-maintain venues for niche sports like softball, beach volleyball, or even swimming.
They became useless immediately after the Olympics left town.
As a result, a decade after Greece spent ~$15 billion to stage the games, some of these once-gleaming venues are crumbling.