Why would someone set up a barrier
in a place like this?

Actually, they discovered the blastia at the bottom
of the oasis, and have just been using it as is.

A nice person in town told me that.

And with it sunk in the oasis, no one could move
it, so I guess they had to leave it where it was.

No one would trudge out into a scorching
wasteland like this just to set up a barrier.

Ah, that explains it.
Guess there's a reason for everything.