1. Unlike LTK, CST never groomed a credible successor. That was his Achilles' heel – his authoritarian ways have rubbed many members the wrong way. (One CEC member was sacked the day after he brought up the need to 'revamp' SDP – this was in '85. Won't mention names.)
2. Lina was not a credible successor. Putting her in PP is like letting Ho Ching replace LHL as PM; the people were pissed and SPP lost the ward.
3. Lina was given a second chance as an NCMP. Though she put in some effort, asked many questions, her limitations were apparent for all to see. After 4 years, who would give her another chance?
The day CST left PP for Bishan-Toa Payoh, he lost PP for good.