Why does the eastern time zone extend so far west?

I am doing a project for science about national parks, and my park is Mammoth Cave in Kentucky. One of the things we have to look up is if it is 10am where i live(in ny state) what time will it b there. according to my research it should be about 2-3 hours behind b/c the longitude difference is 32 degrees, but i know that it is in the central time zone and only one hour behind. why does the eastern time zone extend so much farther than 15 degrees? please give me a source as to where you found this