Hmmm I would agree with you if you were talking about a scandinavian country with a homogenous population or like japan or something.

But Singapore was definitely not a country with little diversity. Chinese is the majority but its malaysian and indian population were 15 percent and 7.5 percent respectively, by percentage there are more malays in singapore than african americans in the US.

One of the main motivations singapore chose to have english as their primary language was not only because its the international business language but rather because they needed an objective third party language. Each language carries its own historical and cultural baggage, if singapore had forced its population to speak chinese there would have been race riots everyday. Instead they chose english were it gave everyone in singapore a level playing field. Which makes this both an economic decision as well as a socio-political decision.

Another snippet is their housing plan which is heavily criticized in the west which forces every ethnicity to live with each other. Like every apartment complex building had to have 15 percent malay and 7.5 indian. Despite it being a bit heavy handed in my view, had they not do that though, there would just have entrenched ethnic enclaves as humans love to divide ourselves into tribal groups.

The founding of singapore is a very spectacular piece of history, I can talk about it all day but i will stop now.