My guess was booking engine was hitlist #1... they wanted to go live with that for whatever reasons ("Shoot the engineer", enhanced revenue opportunities, whatever).

So they've bit off, chewed, swallowed and half regurgitated the biggest/most visible piece of the equation now they have three options:

(1) Leave the website in the (visual) half old/half new thing that just looks unprofessional and sloppy
(2) Go back to the old design until the entirety of the new design is ready to launch... which could be forever and also eliminates options for mass sampling/bug finding (e.g. the award nonsense, searching by fare bucket, etc.) that may not have been noticed until a large population was in front of it either now or 6 months from now.
(3) Push forward with the new, reskin existing pages so that it doesn't look quite as hodgepodge/jarring and then incrementally replace them (based on relative traffic/page views if someone was smart) with new versions over the next several months.