CoinJoin is just a way of doing a transaction. You can get a bunch of bitcoiners together and do a CJ on a bench in the park, over email or Discord.
Whirlpool, a CJ "service" is really only a decentralised protocol. Wallet software that "speaks" this protocol gets together over the network and executes Whirlpool mixing rounds without an intermediary.
TC is open source but the fact that it was deployed as a smart contract means it can be targeted. Sure, you can deploy copies but they will not attract as much liquidity as the "official" one (which is still available, just not over clearnet).
TL;DR: Tornado Cash is *nothing like* CoinJoin.