The road is a noisy place. Cars are soundproofed to deal with that. A loud engine antagonizes everyone not driving but drivers won't even hear it.
Do they make Harleys totally different where you're from? Serious question, maybe your country has noise regulations the US doesn't, or something, so they have to modify them for that market. This isn't at all true in the US.
Cars almost never do unless they've clearly got some severe problems with their mufflers, even though ordinary non emergency cars must represent something like 80% of vehicles I encounter on highways in my city. Even for the loud-bass types, the radius in which I can hear that and the volume is lower than typical "Hog"-alike motorcycles. Motorcycles are also the only non-emergency vehicles that sometimes sound really loud inside my house about 300 meters—and a bunch of trees—from the nearest highway (though that's mostly a couple of jerks who seem to like to race on that stretch of highway every so often, on what sound like racing-style bikes, not Harleys)
Edit: and the idea that a big Harley chopper idling at a stoplight isn't ridiculously loud is absurd. "FUD DUD DUD DUD DUD"
That's why dodge charger owners always put the most loud obnoxious exhaust ever on them. I used to have a Chrysler 300 and it was THE QUIETEST car I've ever been in, by a longshot.