This is because of 'cabotage' rules, where foreign carriers aren't allowed to sell tickets between two domestic destinations, and except for EU carriers flying within EU countries, this is standard practice all over the world.
Qantas has historically had a similar stop in LAX en route to JFK, although new aircraft will allow them to start making the trip non-stop, in an initiative called 'project sunrise.' [1] I believe they are currently routing that flight with a stop in Auckland as QF3, although they are running AKL-JFK as a 5th freedom with pick-up rights in AKL.
I don't think it's true that it's faster to get to Philippines than Guam from the mainland - you just have to transit in Honolulu. SFO-HNL-GUM on United is 14h15, whereas the non-stop SFO-MNL is 14h35. Philippines only offers limited non-stop options to Manila - just LAX, SFO and JFK - so much of the time you'd be connecting either way, and that eliminates any advantages. After all, Honolulu is pretty much on the way to Guam based on the great circle arc. [2]
Qantas has historically had a similar stop in LAX en route to JFK, although new aircraft will allow them to start making the trip non-stop, in an initiative called 'project sunrise.' [1] I believe they are currently routing that flight with a stop in Auckland as QF3, although they are running AKL-JFK as a 5th freedom with pick-up rights in AKL.
I don't think it's true that it's faster to get to Philippines than Guam from the mainland - you just have to transit in Honolulu. SFO-HNL-GUM on United is 14h15, whereas the non-stop SFO-MNL is 14h35. Philippines only offers limited non-stop options to Manila - just LAX, SFO and JFK - so much of the time you'd be connecting either way, and that eliminates any advantages. After all, Honolulu is pretty much on the way to Guam based on the great circle arc. [2]
[1] https://www.qantas.com/au/en/about-us/our-company/fleet/new-...
[2] http://www.gcmap.com/mapui?P=SFO-HNL-GUM,+SFO-MNL