List of all entry/exit/relays are public knowledge and ISPs / govts can use it to block access to tor. How are bridges different in this respect? From my understanding anyone can request for bridge and can get one. Which means it should be possible to write a program to request repeatedly and get list of all bridges in the network and thus be able to add all of them to the block list. So how exactly this is prevented?
From a Tor Blog post, 28 Aug 2019: Tor currently has approximately 1,000 bridges, 600 of which support the obfs4 obfuscation protocol. Unfortunately, these numbers have been stagnant for a while. It's not enough to have many bridges: eventually, all of them could find themselves in block lists. We therefore need a constant trickle of new bridges that aren't blocked anywhere yet. Please run a bridge if you can. Run Tor Bridges.