1) Junus Tan spoke English differently from Singlish because he was born to and raised by English-educated parents and grandfather who studied in English-medium schools. 2) Lee Kuan Yew and other public figures of the time also spoke English in a more crisp, pronounced way resembling "Queen's English" because they were educated in England and interacted with upper-class British individuals. 3) Over time, as more Singaporeans began speaking English as a common language, the formal, precise version became diluted as natural variations developed in everyday usage.

1. Why did Junus Tan’s English sound so
different from Singlish?
Some facts to set the scene:
1. Junus Tan was born to and raised by English-educated parents. Even his grandfather, Lee
Hoon Leong, studied at Raffles Institution – then run and taught by teachers mainly from
England.
2. Hoon Leong gave LKY an English name – Harry. (His siblings include Freddie, Dennis
and Monica.) LKY didn't admire the British nearly as much, and gave none of his
children English names.
3. LKY studied Law in Cambridge, where he no doubt spoke English to English folks, and
came back to Singapore to practice law.
4. LKY's family presumably spoke English or Peranakan Malay at home – which is part of
why he had to labour to get better at Mandarin in his later years.
LKY was raised and groomed to speak English – and not "Singapore English", but something
more akin to "Queen's English". You can tell it from his vocabulary. He read old books quite
prolifically and spoke with lawyers, judges and upper-crust people. He hung out with the Queen.
And it wasn't just LKY, really. If you listen to the other public figures at the time, everybody
spoke English in a more crisp, pronounced way. JBJ comes to mind, but I'm sure you'd also hear
it in the newscasters of the day. And if any of you have had the luxury of being taught English by
an older teacher, you'd notice the difference, too.
I think the English language in Singapore since then has "diluted" a little – I don't mean that in a
bad way, it's just a natural sort of stretching, ebbing and flowing that happens when more and
more people begin to speak a language. The sharp bits get eroded away.