Both are at fault equally, or should we say that none are at fault just that they hold different stances and viewpoints.
Personally felt that CST was a MP that was simply contented to hold onto his PP seat all along, by the time he get to the stage where he felt it was necessary for him to contest a GRC was already too late.
Remembered back then in 2007, SPP and WP had a dinner where they conversed. It was then, he mentioned about the need to take a GRC.
https://www.theonlinecitizen.com/2007/11/04/toc-report-wp-50th-anniversary-dinner/
Perhaps he sensed that LTK himself had plans to lead a team to take on a GRC, thus he felt imboldened to do so in 2011 but he did not carefully thought it out.
The fact, he handed over the PP seat to his wife whom eventually did not perform in Parliament and left no strong impression contributed to SPP's current state.
CSJ on the other hand, was like JBJ. He wanted to did what LTK did, which was to build up their party brand into 1 which could potentially challenge PAP in the future at a national level but he was too impatient and reckless back then.
Can tell that he has mellowed out a bit, power sharing with Paul Tambyah and brining in other qualified candidates has helped him to realise that it was never an one-man show.
Think that Vince Wijeysingha's departure in 2013 over CSJ's decision to contest in the Punggol-East by-election has also struck a nerve too.