The big issue we have seen with contact tracing in this pandemic is that it doesn't catch everyone. Those contacts you didn't find start new chains that you nee

The big issue we have seen with contact tracing in this pandemic is that it doesn't catch everyone. Those contacts you didn't find start new chains that you need to find and disrupt, but doing that requires more tests than are available: People who haven't been traveling are simply denied tests. So you never find those chains, and you get out of control community spread.