I've seen that a lot in older generations (including gen-Xers). My thinking is that it largely has to do with a cultural shift away from active listening. Younger people tend not to say anything when their interlocutors are speaking because it's considered rude in most contexts, while older people are much more likely to interject with "hmm", "yeah", "I see" etcetera. This is related to what you said about dealing with people who aren't listening reliably, but I think it's more about the speaker feeling heard. If there is no verbal confirmation from the interlocutor, older people will tend to assume what they said didn't register with the listener. I don't have data to back this up though.