i'm not saying that they wouldn't pursue expansionism. A half-billion years ago they could have had a thriving colony on our planet. And, as you said, there is a plenty of time to change their mind, literally, and bodies, so planet surface existence isn't a key anymore, or at least it isn't a big deal to let go the planet which has potential for development of new civilization. We're just so low on the development ladder, that we're a national park, designated wilderness, off-limit for the ones who can reach us.