Question

why does a country having a large latitudinal extent have only one standard time

Answer 1

Because there should be no confusion of Time. So the standard time is taken from a place for a whole country. The Indian Standard Time or ist is taken from Mizrapur in UP

Answer 2

Because if the country not have standard time.Railways,airways e.t.c. are doesn't run without this. Because in a whole country there are different times in different time.The standard time is taken from the middle latitude of that country.