The Corporation-that-never-lies (cough... Iraq WMDs... cough...) tells us in an ANIMATION that "The Universe Has A Hard Speed Limit", so other civilizations COULD NOT POSSIBLY REACH US IN ANY NORMAL TIMEFRAME.
https://www.bbc.com/reel/video/p04v97r0/this-video-explains-why-we-cannot-go-faster-than-light
Of course, people a few decades ago were told "NOTHING CAN GO FASTER THAN THE SPEED OF SOUND. IT IS A HARD LIMIT THAT NO PLANE CAN BREAK."