I do not live in Singapore and you most likely do not, either.
Nevertheless I thought you might want to be aware of this because it could be a precursor of things to come here in the USA. In fact, I found this purely by accident. Just because this is for Singapore does not mean another schedule of restrictions, akin to this, could not be in the works right now for America. Anyway, here is the list and it is a LONG list:
There is also obviously the concern these limitations could spread beyond Citi to other credit card issuers.
Note carefully this is prospective and will not go into effect in Singapore until October. Also scroll down and see certain merchants headed for exclusion.
It strikes me there is more than one way to skin a cat and more than one way for CC issuers to lower their cost of rewards. Sure, they could lower rewards percentages across the board. But they also can do what you see there and exempt entirely certain categories of spending while maintaining the rewards percentage where it is now.