For Korean fans, ticketing is three chances, not one

Tickets for a Korean show do not all go on sale at once. There is an order to it, and Korean fans know which round they belong to.
First is the fan club presale. Only official fan club members get in, usually a week to ten days before general sale.
For a popular group, that presale can be finished in three to five minutes. Most of the good seats go here.
Second is the early presale, open to anyone registered with the seller, usually two or three days after the fan club round. If you are not in the fan club, this is realistically your one.
Third is general sale. By then what is left is the far seats or standing remainder.
So an overseas fan who only watches the general sale time has already missed two rounds. Once a show is announced, check the presale dates first.