we took a 50km bike ride, I'd guess we saw about a couple of hundred other people. Mostly on bikes, not surprising as we used a couple of "Swiss Bike" trails, but also on blades, walking and so on. I don't think it makes the Swiss any less lazy than people in the UK though, things are rarely so simple.
You might ask what else there is do here on a Sunday, if you don't go out skiing, walking, climbing, sailing, cycling, horse riding then there's zilch to do, no shops are open and we don't have any of the Alton Towers, Blackpool, Matlock Bath things to do. Noise is banned, you can't mow your lawn and washing cars on the drive isn't allowed and so on. All you can do really is go out and do something interesting.