> And btw in general, what is the meaning of using all those tags if most of them don't get visible on the map?

OpenStreetMap data is *much* more than what is visible in the default layer on osm.org (https://wiki.openstreetmap.org/wiki/OpenStreetMap_Carto). There's also a Cycle Map: https://www.openstreetmap.org/#map=14/47.3918/8.5399&layers=C, or   https://cycle.travel, which uses OpenStreetMap data for routing.
Or for example https://wiki.openstreetmap.org/wiki/CargoRocket, which is especially geared for routing larger bikes, taking into account every detail of barriers.
Hence this data is used *much* more than only the default view here on osm.org