The reason is, Singapore failed to restructure its economy.
I know it's easy to say this, but too many GLCs, connected businesses with RC, whatever C members, made increase in wages difficult as there is a conflict on interest. So if big GLCs and businesses can continue to rely on cheap labours, who is going to improve productivity?
All the stat board initiated R&D, automation and productivity improvement programs are wayang only, (if you got involved before, you will understand). After a few decades of improvement programs, what have we achieved? No follow up, no follow through. Just number games to gain tax incentives.
So today, as a first world country (as they claimed) but relying on cheap labours, they cannot force the locals to accept low wages. So they import FTs. If you want a job, you have to match your asking price with the FTs. Problem solved on their part and we are left to struggle and compete.
The sickening part is, they claim credits (whatever like GDP and so on) and keep increasing their salary.