Moving Grab isn't a big deal, considering Grab's founders are Malaysian Chinese, and likely face indirect discrimination thanks to Malaysia's constitution. Malaysia drove them away, Singapore didn't persuade them.
Edit:- to counter your example, devs are not as highly paid for the living costs of Singapore. And they don't even form part of the upper bracket, which is largely populated by people in finance and management.
Tech salaries are not poor if you compare them to other South East Asia countries (Malaysia, Indonesia, Vietnam, Thailand, etc). If you compare them to other professions in Singapore... then I can't say (I don't know).