I think the Drake equation needs a tweak on the last term 'L', the mean length of time a civilization can communicate. It really needs to be something like the ratio of L over the time period a civilization can arise. If the numerator is 1e5 years and the denominator is 1e9 years. The Drake equation then starts to represent the number of possible civilizations existing in the same time period (a reduction of 10,000X in the example given).