Beyond Korea, SQ (or Singapore side) still owns 5th freedom to one port in Canada and one port in the US. These 5th freedom doesn't have to be continuously used. Set aside the complicated relation between Singapore and Canada, the reason SQ isn't bothered resuming ICN-Canada is because of restricted number of (actually units count) ICN-SIN flights.
To operate SIN-ICN-YVR 3/w, SQ has to suspend 6/w SIN-ICN, because that flight will use 6/w ICN-'wherever' slots. Now that SQ suspends ICN-LAX, SQ can operate one more SIN-ICN which could bring a total of 5 daily flights between two airports. Demand on this route has soared recently. Some LCCs even launched ICN-JHB.
Why they don't add more flights? Because Singapore side wants more 5th freedom out of Korea and Korea doesn't let it happen.