The goblins want it because they are chaotic evil and think raiding is fun. The real reason behind it is whatever Minthara was instructed of by the Absolute, but AFAIK we can never find out about that.
The best answer I can give you is that apparently
Sharran followers attacked the grove and were repelled? (I read on here that you can find a dark justiciar's helmet under the blighted village and that that leads to this revelation but I have never been there myself.
Although I have no idea if that is true.