Interesting. I interpret the question as, why does AA typically use only 2 fare buckets instead of 3 in this cabin? There is no *fixed* relationship among the prices of J, D, and I fares, and depending on how fares are filed, AA can adjust the price *and* availability of any bucket at will, right? So where they're offering only J and D, couldn't they put I at the current price of D and put D in between, enabling finer-grained inventory management? And the *price* of I could be lower on the days they have more trouble filling the cabin. I suppose the current approach exists because from an IT and planning perspective, it's more convenient to keep the price of a given fare class uniform over the week, and then tweak availability.