[plg94]

Not a good point.

A lot of that land is inhabited, or at least owned by citizens or companies. Pretty sure they would be against changing citizenship or losing their land.

And for government owned, uninhabited land: land is worth a lot more than its surface area. You can have natural resource of all kinds underneath – maybe some that are technically or financially not feasible to mine, yet, but may be in a few decades. (Just think of the massive oil fields in the arctic that'll soon be accessible to Canada and Russia) If it's a coastal area it massively extends your country's EEZ – that's why there are a lot of border conflicts around tiny rocks in the ocean. That's also the prime reason why Russia will forever hang onto Sakhalin island. (Plus Japan already is not doing much with Hokkaido, I doubt they'd do anything worthwhile on Sakhalin except forestery and military areas).