I believe the “rationale” (for lack of a better word) is that the land of Greenland will become much more valuable in a post-climate-change world. Much of greenland will become warmer and therefore more comfortable to live in and more suitable for farming. So the idea is to take it now while it’s still largely a chunk of uninhabitable ice rather than wait until later when everybody else is fighting for it too.

At least, that’s my understanding of it.