I noticed a variation of that which wasn't so significant a few years ago: walking along a river path that is for pedestrians and cyclists, many cyclists who appeared to do a day-trip / road-trip (more luggage on their bike) had loudspeakers, too. They thought everyone would benefit from their great taste in music. I know that car drivers do the same (which is even more noisy), but the idea that bike travel / bike commute is less noisy (for others) than a car goes out the window that way.
The music in the countryside ("where there is no-one") will disturb animals and wildlife too, not just other people.
In essence:
People who are so unaware of their surroundings and so sure of themselves that they think everything is enhanced by their taste in music. I, too, see it as marking territory / manspreading by everyone. The noise increases every year with better tech, too. And then you see articles like "living next to a busy road will elevate your blood pressure" and everyone avoids making the connection.
Spatial unawareness and unawareness of a situation, being very self-absorbed; that includes many examples mentioned already, walking next to each other on the pavement and never giving way, standing in the way on principle, not noticing when others need help.
For example in waiting rooms with limited amount of chairs, when someone enters who is less mobile, obviously can't stand for a long time, then often it is not the healthier looking group of people who offer them a seat - I don't just mean doctor's waiting rooms and even when accounting for invisible illnesses there is a clear pattern of the above.
When people live in close proximity, everyone being more considerate would improve health considerably - less stress, less noise, less garbage.