Abuse of the passing lane?

I hear that in Europe, the left lane on freeways, like the Autobahn, is used for passing only. People mostly drive in the right lane. Supposedly, that is the way freeways are intended to work. People ask why that isn't done in America. I think it's because there must be so much more traffic in America that all the lanes are full to a slow crawl. They are all full, at least around urban centers; especially during rush hour. Too many people drive, here in USA. I would guess that in Europe, more people use transit so even the freeways that they do have work better. Maybe they aren't so clogged with traffic. Just my guess, but I've never been to Europe. Yes, mass transit, walking and bicycling does help overall mobility.