Adding on: this is because the PAP in Singapore controls more than two-thirds of parliament [1], and have been able to push through constitutional changes without much consultation [2].

I think the increase in the private-sector requirement for candidates of our presidency (overtly disqualifying Tan Cheng Bock, a former PAP MP who was a candidate for the presidential elections, and is now the leader of an opposition party) slipped past many of our political critics until it was too late; a lot of uproar was focused on the elections being reserved for people from a specific ethnic group [3].

[1] https://en.wikipedia.org/wiki/13th_Parliament_of_Singapore

[2] https://en.wikipedia.org/wiki/Constitution_of_Singapore#Amen...

[3] https://en.wikipedia.org/wiki/Presidential_elections_in_Sing...