The messages are private and that’s what’s most important.
No, that isn’t true. WhatsApp has the same lies. Law enforcement connect communication between users at key times and use it as credible evidence. Why would drug exporter 1 be communicating with drug buyer 1 at the exact time the delivery arrives in the country? Law enforcement doesn’t need to know what was written.
This is what the UK police do with WhatsApp data. Even though they can’t read the messages, they do use the connections of messages to suspicious characters as evidence including date and times, which also puts these other people in the spotlight, opening further investigations.
The UK police can also use ‘stinger’ devices that are “fake” mobile data towers to intercept mobile communications.