etymology - From pharos to lighthouse

Pharos and lighthouse indicate:

• a tall structure topped by a powerful light used as a beacon or signal to aid nautical navigation.

Ngram shows that lighthouse usage has been preferred to that of pharos from the beginning of the 19th century.

Etymology:

Pharos:

• as a word for a lighthouse, 1550s, in reference to the island of Pharos off the coast of Alexandria, on which Ptolemy Philadelphius built a mighty lighthouse.

Lighthouse:

• 1620s, from light (n.) + house (n.). (etymonline)

Is there a reason for the fact that a different term was coined just a few decades later just for such a specific construction and for the fact lighthouse became the more common between the two (nautical paper jargon for instance) ?