1. Because this wasn't any old vulnerability, this was a backdoor placed there intentionally. 2. Because such attacks are rare (or perhaps rarely noticed), with

1. Because this wasn't any old vulnerability, this was a backdoor placed there intentionally. 2. Because such attacks are rare (or perhaps rarely noticed), with the previous high-profile one being a backdoor attempt in the kernel in 2003. 3. Because this is the first high-profile open-source backdoor since tensions began to rise WRT cyber warfare with Russia and China.