Sure the coasts are creating more economic output by far, but people need to eat food. Agriculture is always going to be important, but lot less people are involved in it than ever before. This is part of what's led to the urban/rural divide where the rural folks feel left out - there just aren't as many of them as populations have migrated to cities. This is why people in rural areas feel increasingly left out. It's mostly due to economic forces that are out of their control.
[1] http://jaysonlusk.com/blog/2016/6/26/the-evolution-of-americ...