I think everfree forest was the place where the earth ponies lived before three races united
after heart warming eve, Celestia and Luna ruled and built a "castle of two sisters" there but it separated by ravine
everfree forest is also a place where discord used to rule before, because many ponies live there
but after discord turned into stone, many house were destroyed and lost, plus after Luna turned into Nightmare Moon, Celestia left the castle, and the earth ponies moved to a faraway place
that place became unkempt and became a everfree forest