This blog post sheds some light on what is going on. The Exciting Centennial of Philippine Aviation: PAA To Fly Guam It is about Guam. The bilateral allows three carriers from each country. The US three are Delta, United, and Hawaiian. The Philippines three are PAL, PAL Express and Cebu Pacific. Cebu Pacific is ending flights in December. PAL Express has been dormant. Air Asia Philippines asked to take over PAL Express' authority in August. PAL Express then decided to start service and ask permission for a code share. United responded by complaining about not getting a second slot to MNL or other operational difficulties in flying to MNL.

On another note, the limitation of three carriers with the bilateral may have been one of the factors in Delta keeping one flight to MNL, along with the US Govt. contract and the lack of slots at MNL for KAL