FYI since you appear to be stuck on this point. Unobtainium is used in science and engineering for a material that can meet requirements but is too expensive, yet to be discovered or inaccessible by any means. https://en.m.wikipedia.org/wiki/Unobtainium
That being said bluvatar was a cookie cutter adventure story. Nothing special but it has mass appeal. For those of us who enjoy movies and television typically acknowledge that ATLA has a rich story, tons of depth and conveyed meanings and somehow doesn't take itself to seriously. ATLA is a work of art, bluvatar was a cash grab.
I imagine it's similar to growing a garden or maintaining lawns and aquariums. It could be earths hobby to cultivate critters ¯\(ツ)/¯