[brando]

I think it was because pretty well no-one in the German forces expected SeeLowe to go ahead for logistical reasons unless Goring's fliers were able to gain mastery of Britain's airspace. This they were unable to do and it cost them pretty dearly.
From the German side it was a fiasco as far as the overall plan to create the conditions for the seaborne invasion was concerned and, when the weather closed down in the Autumn, there had been no lasting destruction of the main targets, i.e. 11 Group's airbases, the Chain Home radar network, and the military bases.
The Luftwaffe had been badly led by Der Eisener and Hitler had turned his sights on the East, so the air assault and the invasion were just allowed to slide.

In hindsight it can be seen that a) properly led the long air battle could have been won, and b) letting Britain off the hook set the stage for what came next.

It's also worth noting that the air assault didn't end when day-bombing was curtailed. Night-bombing remained as another serious threat and continued, but no serious attack on the fighter bases was delivered. Thus I think the German population was lulled into thinking that nothing decisive had occurred - but, for the reasons mentioned, we knew we had driven off the most serious attacks on our shores. And they never recurred, ever. Definitely a cause for celebration in my book!

B