I think your perception of what is being played inside the earbuds may be why you're confused about this. Around here it's extremely common for people to keep their earbuds in for short conversations, but everyone will pause and activate surrounding sounds while they talk. There are obviously assholes who don't, but in general it's completely normal to assume someone wearing earbuds is listening to you.
Contradictory to your experience with it being young people who wouldn't listen to you it tends to be the 45ish business man who continues to talk on their phone in my experience.
I think it's a little disingenuous for you to take what I said out of the context I said it in, but you're right as far as it's in my anecdotal experience. Which is why I said "around here", but I guess I could've made it even clearer.
Contradictory to your experience with it being young people who wouldn't listen to you it tends to be the 45ish business man who continues to talk on their phone in my experience.