for HKG to TPE route, there are already 5 carriers flying this route. They have more frequency than SQ. There are mostly business passengers on this route. They will choose more than 10 flights a day of CX and CI than 3 times a week of SQ.
Therefore, SQ and Japan asian dropped this route in recent years after KA and EVA got rights to fly.

The demand for SIN to HKG is stable but too many low cost carriers.