Why is it inconvenient to use the local time?

Local time is very convenient for the local population, because it corresponds to the real day and night. But on a national scale, or even on a scale of some regions, it is not convenient to use local time, because it changes everywhere. For example, it is inconvenient in the field of mass media, because television channels either need to adjust, or all adjust to the same time. Also inconvenient in terms of trains. The schedule for all regions should be at the same time so that there is no confusion among people.