I have my own theory.
Firstly, Singaporeans are busy with work or school.
They themselves dont have time to do sports, or even have sex,
according to survey.
As such, sports is a distant realm in their life.
Secondly, since you mentioned soccer, another complementary theory
for this:
It is perhaps not nice to say, but, I think soccer in Singapore is
un-glam.
It is not nice to dwelve deeper into it.
Meat Pao.