There is something unsatisfying about an approach in which, no matter how hard we look, no matter how thoroughly we search, the absence of ETCs is explained simply by saying they don’t want us to see them. (I can explain the lack of observational evidence for fairies at the bottom of my garden by saying they become invisible whenever people look their way. Irrespective of whether fairies exist, this is a poor sort of explanation from a scientific standpoint.)
