Each location has its own local time. This didn't matter for most of history.

Once we had trains there was a need to ensure that clocks were synchronised to ensure that trains departed at the same time for everyone concerned. These times meant there was a need to have standardised time over a large area.

WWI in Germany saw the need to make maximum use of available daylight in factories and this practice of daylight saving was quickly adopted in high latitude locations. In equatorial locations there is no point in daylight saving as sunrise and sunset don't vary much throughout the year.