If you were able to monitor texts of some random phone number, you might not know their identities at this moment, but given enough time you would have enough info to figure it out. Who else they text, what time they text, the actual content of their texts, etc

Public transactions is an attack vector. Everyone you transact with can at least see partial balances, see where it came from, and follow it going forward. Even if you coinjoin every single transaction you have to forever maintain it. One future consolidation mistake undoes everything. Even bitcoin privacy wizard make mistakes.

99% of people aren't going to coinjoin let alone every transaction.