An hour divided into 60 minutes because it is based on the sexagesimal system of notation, a system based on the number 60 that predates the decimal system.
It was developed about 2400 B.C. by the Sumerians.
Since ancient times, the sexagesimal system has been used to divide circles into 360 degrees (60 x 6), each degree into 60 minutes, each minute into 60 seconds.
Because clocks have round faces, it seemed sensible to apply the system to the measurement of time.