Because the reason they implemented the HDB mass housing program had nothing to do with them being authoritarian or a city state. They are just nice commieblocks.
Lee Kuan Yew was afraid of the domestic communist opposition. This was a popular policy of theirs and they were getting dangerously close to power,so he ripped it off. It's a formula for staying in power that served him well.
Back when western leaders were deathly afraid of communists they used to build public housing as well. Then they stopped. Singapore continued.
