Everything about the A320 design was optimised to make the aircraft economical to operate so minimising any extra air demand would help with the overall economy.
The avionics vent system is over engineered but think of the heat produced by all of those 1980s era computer boxes and also the basic flight control of the aircraft is totally reliant upon them.
I was told by an old avionics engineer that one of the early operators had an avionics vent problem in flight and ended up with only one of the fbw computers operating.