It doesn't take a glance at a map of the Timezones to see that using anything other than ONE is necessary.
I use UTC simply as an example (ref: Wikipedia)
"Coordinated Universal Time (UTC) is the primary time standard by which the world regulates clocks and time. It is one of several closely related successors to Greenwich Mean Time (GMT)."
Using a time that changes only ONCE when traveled over (example: International Date Line) eliminates any need to process anything more than the exact same time whether it's East Coast, West Coast, etc...
This obviously saves the time and complexity needed to transform times to different zones, reduces possibility for error, reduces the data set needed to process - the whole country won't change overnight but we need to start somewhere to get there.