That is because for international recruiters, it is immaterial. Foreign talents can only work here on a work pass, (as noted earlier). Work Pass holders are not subject to CPF so no need to bring it up just to confuse people. The only way is if the potential employee makes the comment that eventually they would like to obtain PR. This process will take a minimum of 4 years and most probably 5+ before you could get PR assuming you are the right flavour for the government's ideal demographic makeup.
Then, if they know their client (the future employer of the candidate) well enough, They might tell you that if you take up PR, your contract may have a clause in it specifying that by taking up PR, your salary contract may be renegotiated (downwards) to allow for the employer's additional costs for their portion of CPF contributions (17%). This would be a double whammy as you would go from $5000 basic & take home to $3320 take home. Additionally, by becoming a PR, you also would lose any housing allowance, school allowances, etc that you might be getting in addition to the previous basic allowances. You also would need to include all allowances in calculation of your income taxes both here and at home, depending on whether you have a tax treaty between your country and Singapore - the US doesn't - there you need to use the Income Earned Abroad exclusion and/or Tax credits. Hope that helps clear some of the fog.