Because at least if you found saver availability, it is at a decent award level. AA’s tiers, for the time being, only apply to AAnytime awards. As a DL refugee, where you will see the big squeeze is long haul, premium cabin awards where there is a considerable difference between cash and award fares. Business class saver awards can be had for roughly double the cost of a saver economy award. That sort of multiplier is nearly unheard of with cash fares.

Advance purchase restrictions will also come into play. It’s long been possible to get a seat in economy at saver levels when the plane was empty, but because of advance purchase restrictions the cash fare was quite high. You can be sure this is a primary target of such dynamic award pricing efforts too.