Why every town once kept its own time.
Until the 19th century, each town set its clocks by local solar noon: London and Bristol differed by about 10 minutes. Timetables became unreadable. British railways switched to Greenwich time from 1840, nearly all by 1847. Germany legally adopted Central European Time on 1 April 1893. Your time zone is a child of the railway.
Useful: Standards usually appear only when a new network forces them.
Source: en.wikipedia.org