Maybe it's not Singapore that's an outlier, but the US? Delivery in Spain, Portugal, and other European countries is by motorcycle.

I believe in the US, a car driving license is fairly easy to get and used cars are very cheap. Plus, given the driving culture, I assume that in the US people just don't think about motorcycles unlike in Europe or Asia as a viable way to get around.

It's a safety in numbers thing. When there are 90 motorbikes and 20 cars at an intersection it's a lot safer to be riding a motorbike than in the US where you might see one or two motorbikes on your commute.