And let's not forget Singapore's strategic location in the center of world's busiest shipping lane too. That's why Singapore is strongly against the construction or Kra canal, which could shorten the route by ~1200 km bypassing Malacca straight:
Whilst it depends a bit which ships you count- the world’s busiest shipping lane is generally regarded to be the Straits of Dover with about 400 commercial transits per day. [1]
1. https://en.m.wikipedia.org/wiki/Strait_of_Dover