Why do poll closing vary wildly by state?

[JG]

In the 2016 election, the polls closed in Indiana and Kentucky at 6pm local time, but in some other states, notably New York, polls are open all the way to 9pm.

Why do the poll closing times vary so much from state to state, and why don't the poll closings just end at the same time locally, and just go west state-to-state?

Because some states are actively trying to supress votes (ie Indiana).