It's capacity is 1200 pph, about the same as FOP. If you never stopped, that means the line was light, and those in it never had time to stop and pack in a bit. After a storm, if those entering the queues are 1200 an hour, which is a healthy 20 per minute, the line will never really materialize.
It isn't 2000 an hour like Mansion, Mermaid,or Pirates. Although it is larger than the new Disney standard like Frozen, 7 Dwarfs and NRJ. It seems even at least one Star Wars ride will have a 1000ish pph throughput.
Pandora is popular, but it's a low throughput ride that makes it seem much more popular than it is. People still unknowingly get in the NRJ line, not realizing it's non FP capacity is like 200 an hour.
And I'd assume FOP gives out FPs based on four theater operations, or at least 3. It seems many days it has issues, so its wait balloons quickly.
And the rest of AK is busy because of the crappiness of FP+. Folks who get that coveted FOP FP also have to burn their other two FPs for the day at AK. They can either spend a good chunk of the day at AK, and get 3 quick rides, or spend the day elsewhere in standby after FOP. Of course they are going to stay at AK and ride their collection of rides, and quickly realize Dinosaur actually has air conditioning, and rush over there to cool off, and after doing that for an hour, they can ride a ride.