Contact tracing is great for diseases like SARS and MERS, but it just doesn't seem to work adequately for this coronavirus Even Singapore is being forced to enact stricter and stricter lockdown measures. Also, you're not even going to get it to work as well as it did in Singapore unless the virus is coming from a known, external set of sources that allow you to narrow down the pool of potential cases.
(Public Health England in the UK had a fairly competent, though not totalitarian-level, contact tracing program. They stopped a while back because it became evident that despite their best efforts, the disease was becoming so widespread that it was reaching the limit of their contact tracing resources and most of the infections were probably unknown community spread that couldn't be found via contact tracing anyway. Other countries are likely similar.)
(Public Health England in the UK had a fairly competent, though not totalitarian-level, contact tracing program. They stopped a while back because it became evident that despite their best efforts, the disease was becoming so widespread that it was reaching the limit of their contact tracing resources and most of the infections were probably unknown community spread that couldn't be found via contact tracing anyway. Other countries are likely similar.)