Frankly speaking, foreigners have no qualm becoming PR since they generally don't lose anything (especially those employed on local terms) and yet get to enjoy almost all benefits that Singapore Citizens can get, minus the new HDB flat and National Service. Try asking them to convert to Citizens and many excuses will come out such as "Mmm, Ahhh, Nooooo, all my relatives, parents all still in home country", "too attached to home country, emotion burden, cannot lah", ...
(Most of them also register their kids borned in Singapore as their own native country's citizen rather than Singapore citizen). If that is the case, why their kids also have priority for registration to primary school etc? Give people impression that Singapore Citizen is the cheapest thing on earth? (their own countries' citizen is more valuable since by being a Singapore PR they already can enjoy almost all the benefits without being a Singapore Citizen).