Why Indonesia’s tsunamis are so deadly

The magnitude 7.5 earthquake, and subsequent tsunami, that struck Indonesia days ago has resulted in at least 1,200 deaths.
Authorities are still gauging the extent of the damage, but it’s clear the earthquake and tsunami had a devastating effect on the Sulawesi region, particularly the city of Palu.
It’s not the first time earthquakes have caused mass destruction and death in Indonesia. The tsunamis that follow are particularly damaging. But why?