The big difference between SG compared to many other places, is very simple.
SG boasts of all the expensive installations & buildings, and man made sanctuaries. SG boasts about being the 1st in asia to have many 'attractions'.
Conclusion, tourists rather visit the real things that have history & character in it, than to spend $ visiting places that've been man-made, and lack substance in it. So, its obvious that some come here for transit to other neighbouring countries & islands. Some may just spend 1 or 2 days here for some shopping, and that's pretty much all there is to do in SG.
8 out of 10 foreign friends of mine, use SG as transiting point to visit, M'sia, Indon, Thailand etc. The remaining 2 are here to learn a new language, and work part time to cut back losses on rental.