> Passing isn't something that is only the responsibility of the passer, that of course is absurd. Most people don't walk on the very edge of a path,

Interesting difference between Canadians and Spanish people then, very interesting. Here it's expected you don't walk in the middle if you can, at least in metropolitan areas where people have very different walking speed. If you have to say something in order to pass the person, then the other person is already doing something wrong. Most people I see with headphones are indeed almost always walking very much on the sides, exactly so they are not in the way and don't need to be bothered.

> personal transportation devices (scooters, e-unicycles) and other things (roller blades, bikes, skateboards) where often the only sound is the noise of the wheels on the sidewalk / pavement making a quiet hiss / rumble

I guess this is a more practical difference, here all vehicles (including scooters, bicycles, and everything that doesn't have two meat legs) have dedicated streets/lanes, or use normal roads where cars go. None of those vehicles go at the same street/pavement where pedestrians go, so I don't think headphone-wearing pedestrians have to worry about the same thing as the Toronto people seemingly have to watch out for. You could walk blindfolded more or less in central Barcelona, and not get close to being hit by any bicycles or scooters. In fact, there are tons of blind people seemingly navigating the city just well :)

Hope you get more modern car-alternative infrastructure in the soon future! It helps a lot to separate a whole host of traffic you don't want with pedestrians, and is easily worth the investment.