I am guess they are harvesting to much wood in the Fairy Country, so now the fairies are pissed and killing non-fairies. That would explain why they have to evacuate all the non-fairies.
@Vasqueztion I imagine if the fairy kingdom was destroyed, the fairies met with a genocide, and the queen appeared in front of the MC half dead, asking for help, he would kick her in the head, complaining about breaking the promise.
it seems that all the intentionally irreparable damage from logging is what i'd call bad game design. because like it or not, you can't teach complicated concepts like ecology and expect random pubbies to abide by it
Even if they could, they would either have to have miraculous growth speeds for trees, be it effectively regeneration or time reversal with noone planting new and the old stumps regrowing, or if they somehow added in treeplanting, they would need miraculous growth as well, but not many would do it, and the stumps would need to be dealt with.