Because the place name in Xiamen near the airport is called Gaoqi. The word "qi" in Gaoqi in Xiamen evolved from the word "畕", which refers to the winding embankment on the seaside.
But the airport built by the Japanese in the past is not the same as the one built later. The later Gaoqi International Airport was rebuilt.
This is a map from the Qianlong period of the Qing Dynasty, when the place name Gaoqi existed.