The German's had no appreciable night fighter force, compared to their day fighter numbers, and night fighter production did not really result in any substantial increase (although the technology they employed did). BC hardly bottled any of the Luftwaffe up. AAA was seen as the primary means of defence against airborne attack, particularly against the relatively low flying RAF. It was the withdrawal of day fighters (because that's mainly what they had) from other theatres to counter the daylight bombing offensive that produced the most effect on the Luftwaffe's ability to project force in those areas. The USAAF flew too high for most of the German AAA to be effective, and thus fighters were the only other alternative, even though by that time their performance at those altitudes was inferior to the Allied equipment.