How common are cancelled landing attempts?
I could see the airport as clearly as one can see an airport in thick fog...


If you saw the runway by looking down from your passenger seat as the airplane passed over the airport on the missed approach, you were looking only through an amount of fog approximately equal to the altitude of the aircraft above the ground. For purposes of discussion, let's say that was 50 meters. The pilot, however, is looking through the front windshield trying to see the runway ahead to position himself for the landing. If he was on a standard 3 degree approach slope, that would mean he is having to look through nearly a kilometer (beware of old man doing math in his head) of fog.

Years ago when I flew for a commuter, I often had to make multiple missed approaches at Pullman, WA, USA in snow storms. My rule was that I would try 3 times before diverting. When we diverted we would often get complaints from passengers about not landing because they could see the airport as we passed over it. I could, too, but only through the cockpit side window, and with featureless snow covered rolling hills, there was no way to position for the landing without losing sight of the airport.


  What might have caused the pilot to actually land the second time but not the first?


The thickness of fog or how hard it's snowing or raining is constantly changing. Try again and you may be able to see what you couldn't before. If you can't, maybe try a third time and get lucky. Trying more that that would mean eating into your fuel reserve to get to your alternate, and, just as importantly in my view, pilot fatigue becomes a problem. Plus, you're beginning to seriously blow your schedule.