Now that I've been, I can say exactly why:
The endless changing vistas of sights never before seen and not to be seen anywhere else on earth.
So many unique ecosystems within kilometers of another.
So many waterfalls that most don't even have a name.
Landscapes as if the Trinity had a jolly good creative time.
The lupine--bluebonnets on steroids.
Mountains. Deserts. Oceans. Geysers. Glaciers. Iceberg lagoons.
Moss covered rocks. Black sand. Painted mountainsides.
Sheep. Black. White. Striped. Spotted. Frolicking lambs that come in pairs.
Colors in nature with unique brightness and hues and layers and textures.
Weather literally changing within seconds and minutes from snow to sun to rain to wind.
Reindeer and puffins.
Waffles for breakfast.
Chocolate squares served with hot drinks.
Espresso available in the most unlikely places.
Containers of water always on the table at meals
Water so pure that no one who lives here would think of buying bottled water.
Surprises of art, particularly murals and sculptures, in the most unexpected places.
The clear love of beauty expressed in the most quotidian details of everyday life.
Speaking of everyday life, the WC's are the cleanest, warmest I've ever been in; even at camping grounds and gas stations, no matter how remote.
Wifi in every building. Generous placement of electric outlets.
People willing to speak English.
Since we only drove half the Ring Road, south and east and back, planned that way in order to get better May weather (which we did) and to be able to see where we'd been, and have a second chance to do and see, we've already talked about returning, this time going west and north.
But now, the trip home begins.