It still gets a large portion of its funding from the USG
Tor's main purpose is to allow agents of US intelligence agencies to communicate back with the home base.
"Giving free access to the Internet being a powerful tool for undermining authoritarian regimes" makes it harder for an adversary to focus solely on intelligence agency agent traffic.
I'm not saying Tor is backdoored or monitored, though it's heavily monitored.
When enjoying the benefits of Tor, it's wise to also remember Tor's main purpose.