It’s difficult to pinpoint the exact reasons but Singapore constructed to be a nationalistic/patriotic country. Children are made to sing the National anthem and recite the National pledge every morning in school, sent to participate in the National Parade at least once in their lives, constantly reminded of the fragility of the Nation from foreign influences (Total Defence), all males are conscripted into what is called National Service for a period of two years. Coupled with the lack of civil and political liberties, resulting in the infantilization of the citizens, even justified criticism of the country is often considered as an attack on the country and/or their identity. The conflation of the state with the government with the one-party authoritarian system makes that even worse. [0]
[0] https://www.cambridge.org/us/universitypress/subjects/politi...