The unencrypted metadata is a transaction between Bitcoin addresses, not mapped to any identity. This is similar to the Bitcoin network, where we just know that addresses contain a certain amount of Bitcoin but we cannot identify who the address belongs to. Compared to privacy apps such as Signal or Telegram, they have some metadata about users.
One should think of a message as a small transaction that embeds some encrypted data on the blockchain. Miners are including messages on blocks because they get paid a small miner fee. These transactions are uncensorable because the Bitcoin network is uncensorable. Traffic of apps such as Telegram can be identified and blocked as Russia has done so in the past.