If the goal of AF is to be constantly happy, why not just remain in strong second Jhana as it offers " When this state is really cultivated, the intensity of the pleasure of this state can become pretty much as strong as you can stand it." ?

Jhana is impermanent and not to mention cruder and less refined than the more transcendental insight into the true nature of phenomena.  It temporarily suppresses the lhindrances of sense desire, ill will, sloth/torpor, restlessness and doubt in addition to giving a nice temporary bliss wave and a temporary peace of mind.

You would also have to keep sitting for several hours each day to keep the bliss up and the hindrances suppressed.  This might be good if you're a monk, but even if you were a monk the primary purpose of meditation is liberation (insight into the three characteristics) and not jhana.  It's much better to have the peace of mind as the default resting place rather than the place you can keep moving into, but are unable to become stabilized within.

I think you guys have missed the lessons of jhana.  Thor, you're on the right track with your thinking, here.  If you know how to reach the jhanas, then you have learned what the 5 hindrances are experientially and you can begin working on them during the day.  In my experience, the jhanas will manifest spontaneously during the day if you're practicing mindfulness correctly.  Nikolai (from the Hamilton Project) had some interesting practices post AF he was doing where the arupa jhanas were appearing during the day.  If I'm remembering correctly, he and Tarin posted some interesting discussions on there about how the PCE related to the arupa jhanas. 

Anyway, jhana practice should spill over into daily life!  You can use the techniques you use to get into jhana when you encounter problems during the day and this will bring you back to mindfulness more quickly.