This is not really true. The truth is because there were no credible oppo leaders capable of surpassing LKY in swaying the sinkies to opt for an alternative Govt...until LKY went into retirement. By then, WP in Hougang managed to convince sinkies that defeating papees is not an invincible task. All it takes is for more capable sinkies to come forward to join oppo parties and challenge the papees.
It started in GE2011 with the first fall of the Aljunied GRC and will continue as well in GE2016. The final collapse of the papees is inevitable in the future and LKY might die of seizure if he were still alive to see papees getting booted out of the Govt.