Murica the United States, we have the Eastern, Central, Mountain and Pacific time zones.
For live events, like sports, the starting time for television broadcast would be different for all time zones - 9 PM Eastern, 8 PM Central, 6 PM Pacific - so that it's live for all viewers.
Regular taped shows usually start at the same time in the East and Pacific time zones (i.e. 9:00 PM) but the Central time is usually an hour earlier so it's on the same time as Eastern (8:00 PM Central).
This is why we have questions like: What does 7c mean in this poster?
Why is this? Do the Central Time people go to bed an hour earlier? Or is this based on old technology where it wasn't worth the effort to delay everything for one hour?