TSL less popular than GKY.
Few possible scenarios assuming this was decided after WP not contesting MP.
GKY is known best buddy of LW.
These are the possible scenarios.
1. GKY volunteered to go punggol so that tch can retire and to support LW. In exchange, TSL was then assigned to CCK to cover for him.
2. TSL was assigned to punggol but he declined as it's much higher risk. LW then assigned his buddy to support him. Then assign TSL to go CCK.
Scenario 1 looks more likely but it's in fact very risky. Any traffic jam means GG.