What those don't address is quantity per category. There's way more cars than motorbikes on the roads (in Switzerland and most EU/North America areas).

This is an important factor. Most of the comments seem to be fixating on motorbikes as one of the biggest sources of noise pollution based on sound intensity. I understand this, but it doesn't speak to my experience.

From my apartment I can rarely hear a motorbike, while the car noise is near-constant. I sometimes close my windows during the day specifically because of this. I find it overstimulating not due to its intensity, but due to the unending nature of it. 'That basic rumble you can never escape' is a good way to put it.

So, for someone in the same situation (which would be most people living in a city) removing noise caused by cars would lead to a much more significant quality-of-life improvement compared to removing its motorbike counterpart. Even if motorbikes are louder.