Censorship on the clearnet operates through several mechanisms: DNS filtering blocks domain resolution, IP blocking prevents connections to known server addresses, and BGP hijacking redirects traffic at the network level. Tor hidden services are immune to all three. They use no DNS - .onion addresses are resolved within the Tor network. They have no public IP address. And Tor's encrypted, multi-hop routing prevents network-level interception.
Even in countries that attempt to block Tor itself, the network provides bridge relays and pluggable transports that disguise Tor traffic as ordinary HTTPS, making it extremely difficult to block without shutting down the entire internet. Readers in China, Iran, Russia, and other censoring nations can access your .onion site using Tor with bridges.
The .onion addressing system itself is censorship-resistant. No registrar can seize your address, no ICANN policy can revoke it, and no court order can redirect it. Your .onion address is derived from your cryptographic key, and as long as you control that key, you control the address. This is a fundamental architectural advantage over clearnet hosting.