Why do people in the Spanish-speaking world often call Chile's capital city Santiago de Chile?

Santiago has coasts on both the Atlantic and Pacific Oceans.
The national University of San Marcos is in Santiago.
A city in Spain also has Santiago in its name.

People in the Spanish-speaking world often call Chile's capital city "Santiago de Chile" to differentiate it from other cities with similar names, specifically Santiago de Compostela in Spain. By adding "de Chile" (meaning 'of Chile') after "Santiago," it specifies that they are referring to the city in Chile rather than the one in Spain. This helps avoid confusion and clearly identifies which Santiago is being mentioned.