A common misconception is that Daylight Savings Time exists so the farming industry could have more evening hours, but in fact, agriculture has long opposed DST (and for awhile there, they were successful at overturning the practice and returning the United States to "God's Time").
DST as we know it was actually instituted in the U.S. in 1918 to support war-fighting efforts, and we were late to the game; the German Empire and Austria-Hungary began DST in 1916, and one by one other countries began to follow suit. It was generally abandoned after WWI, but reinstated during WWII.
Once the war was over, there was no uniformity throughout the U.S. as to whether or not states would adopt DST permanently. It wasn't until 1966 that Congress legislated DST for 48 states through the Uniform Time Act.
Arizona (save for the Navajo Indian Reservation) does not observe DST because extending daylight hours during summer increases energy consumption; people want the AC on when they're active. Hawaii also opted out of the Uniform Time Act; because of Hawaii's latitude, there isn't much of a difference in the length of days throughout the year anyway.
Check out the video for a quick look at the history of DST in the United States: