Do we know what they're saying, though?

Intelligence agents throughout all of history have utilized the most public of communications as a mode to transmit messages that go totally unnoticed by most.

That said, we pick it out anywhere we see weirdness. That doesn't mean they are actually comms, or at least not in the way we would think. Just take a look at all that image decryption stuff people are stumbling on; the messages are hidden in plain sight so the deep-state doesn't even know they exist (or where, if nothing else).

The messages also don't need to be included in the actual tweet; could be that some just include key words that tell other people in the loop where to look for the next message.

The point is, there are a lot of ways of secure communications. Just because we catch on a bit doesn't mean we know even remotely the contents; similarly, just because we're granted the intel to know some of the messages, that doesn't mean all of them.