Well they don't actually, Tor especially has enormous amounts of government nodes so they can trace and log exactly what and who. And all of those still rely on the IP network which always will allow logging without you ever knowing, it's just math really, the proof of not-logged is just impossible.

These technologies give privacy and anonymity under normal conditions, but they do not prevent anyone from logging ciphertexts. If someone has logged ciphertext, and the government subponies someone to divulge their private key and subponies whoever has the ciphertext, those ciphertexts as good as plain text.