Time + vs -
I believe this is one reason: if you generally are ready for sleep
at 10pm eastern time and travel
to the west coast, you would be ready for sleep at 7pm pacific time; not too hard to stay awake a few more hours.
If you are ready to sleep at 10pm pacific time and travel to east coast, your body would not be ready to sleep until 1am. Trying to sleep 3 hours before you are ready can be difficult.