Why would surrounding countries not claim accessible, habitable, and unclaimed land?
I am designing a world for high-magic, epic campaign for D&D 5e. I really am feeling this map, and am trying to figure out how the different countries would interact. Right now I have nothing planned for different governments or societies, I am just trying to figure out if this can work.
That island in the center is what the title is referring to. Why would the surrounding countries, who have been at war and have very easy access to water travel (large navies, war ships, etc), not make attempts to claim that white island in the center?
Right now all the answers for related questions are things like "it offers no resources" (I would like it to actually be resource rich), "it's in a bad spot" (it's closer than other successful wars have been fought), or "religious taboo" (this feels almost like a cop-out).
Does anyone have any thoughts? I could think that maybe it was monster-infested, the countries are worried they couldn't hold it, or things like that. However, for being monster-infested, they have some pretty strong mages and fighters, why not fight them off? For the too big to hold, why not just hold part of it that is closest to you and then expand slowly as you get more manpower and resources from controlling it in the first place?
Right now I'd be okay with there being people there or not, but I am unsure if there is a good reason that I like.
Ideas or counterpoints would be appreciated! Thanks all :)
Edit to clarify the context for D&D, sorry I didn't elaborate. 878
It's essentially medieval technology but with better metals and boats but no gunpowder. However, they do have basic lamp oils and the like. Long distance communication is possible by magic as well. Non-magic users can keep up with magic users in a fight, but only very very well trained non-magic users. In a fight with your average soldier vs your average magic-user, the magic-user will win most of the time. 523