The airlines should not care just about most of their customers. They should care about those customers whose incentives could be affected the most by the program. If points are equal to cash, then customer loyalty is not encouraged that much, and their incentives to be loyal are not affected much. On the other hand, having a miles based program can significantly affect the incentives of the road warriors to stay with the given program even if a competitor's program occasionally offers better cash prices. And even for the infrequent customers, DL miles don't expire, and they can collect them via credit card purchases and other promotions, and so that the free ticket is not that far away.
When Southwest changed their program, they made a claim to the effect that it was an improvement for most of their customers. This was true: Most customers fly so infrequently that their credits would expire before they reached the necessary count of 16.
I can see DL making a similar claim. For the infrequent flyer, the current program offers negligible value. A cash balance program (points being nearly equivalent to money) actually rewards very infrequent fliers, which miles programs don't do so well.
Naturally FTers, who were mostly winners who gamed the old system, become losers under the new non-gameable (is that a word?) system. So we will raise quite a fuss. The airlines know this and they don't really care.