Because Sri Lanka has more productive people than all other countries in South Asia. Simple as that.Syria has less people, so less to worry about. More resources. More cleaner environment. It has everything to do with population. Why do you think Sri Lanka has the highest standard of living in South Asia?
Pakistan has a bigger population as well as bigger resources than Syria, bigger land mass, more fertile land, rivers, longer coastline as well a bigger work force.
Now go look up the definition of per capita.