It’s selection bias. Almost nobody does it, but for those odd people who do, everyone gets to hear them.

Just like the people who speed, weave and pass everyone in traffic; there’s relatively few of them, but they affect everyone, so it feels like more people are doing it than actually are.

All it takes is for one person who normally uses headphones to have their batteries die, forget the headphones, or something else totally explainable, and suddenly they can be affecting hundreds or even thousands of people.

Of course, there are also other people who just regularly talk loudly on their phones and have the speaker cranked to max; I suspect these are people with ear/hearing issues that find headphones uncomfortable and don’t realize how noisy they’re being because they can’t hear it themselves when others do it (because of hearing issues or because they never shut up).