It’s highly likely they use some form of communication completely inscrutable to us and our way of searching, limited to radio waves, is so utterly primitive they’re effectively invisible to us.

Like a culture who uses smoke signals looking at LA and going “I dunno man, all I see is screaming…”

We’re already on the edge of getting past radio waves ourselves, fiber optics, lasers, quantum communication…

https://en.m.wikipedia.org/wiki/Fiber-optic_communication

https://en.m.wikipedia.org/wiki/Laser_communication_in_space

https://en.m.wikipedia.org/wiki/Quantum_channel

Continuing to search for radio waves seems silly when our own use of them will seem limited to 200 years, tops.