Exactly, This is just how our brains work. It is surprisingly how much stuff we miss because it isn't relivent to our lives. It is like those videos of the man in the gorilla suit in the background. You're so focused on the subject of the video your missing a gorilla walking past in the background.
I notice this about words or phrases as well. If I pay attention to what I think is an uncommon word or phrase. Suddenly everyone I know friends, family and coworkers all "start" using that word or phrase. Now maybe they have started using it but I think it is more likely they have always been using that word/phrase but I have just not given it much thought.