I am searching for flight from Hokkaido, after quick search, if I am to fly from Taiwan to Hokkaido (HKD/CTS/AKJ), it would cost me 17000-19000NTD(round trip), while flying to other Japanese airports will only cost me 4000-13000NTD (only consider those airports with direct flights). Similarly, if I am flying from Hong Kong to Japan, round trip flight to CTS would cost near 5000HKD at least, while round trip ticket to almost all other airports in Japan with direct flight from Hong Kong can be obtained with less than 2000HKD.
Then, I think it might have to do with the distance, thus I went onto check the price to fly from Sakhalin (Russia) to Japan, which it turn out that flying to CTS will still cost more than to NRT despite less than half the distance.
And it's not related to the demand either as some carriers have to cut their TPE-HKD route frequency and swotch to smaller plane due to oversupply.
So why are flights to Hokkaido more expensive? Is it related to the cost to use those airports?