The biggest issue I've found with pfs scenarios, especially the newer ones, is that the writers don't trust the GMs. If the writer trusted the GM, they'd give each NPC a set of motives and goals. Then each GM would be able to play out the encounters to react to their players' approach. Instead, scenarios are written with rigid instructions, npcs are forced to attack the players in obviously stupid situations. Only in pfs would two bandits think it a great idea to try robbing 6 heavily armed individuals, and fight to the death.
It has to be hard to write an adventure that has 4-6 encounters along with something to think about or solve. If you write in motivations and leave it up to GMs, you run the risk of NPCs acting intelligently, which will just screw the game up.
For example, PFS strawman scenario #1: A group of orcs steal a wand and try to escape back to "Orctown" with it so that they can sell it to an Orc shaman. PC's win by recovering the wand.
In a PFS scenario, the orcs would camp in a cave complex and spread out in random patches through a cave system so that the party could attack them in their sleep and have several encounters.
If a GM just had motivations, the orcs would split into two groups, each thinking it had the wand. They would ride hard, raid a farm and steal fresh horses, and then continue riding. They, working for a wizard, would bring a spell scroll that could conceal their tracks, or hell, just teleport the wand back to the wizard. Maybe the orcs would take a hostage or even hire guards. In any case, they would never split up and their would only be a single encounter with the orcs in a day, when or lose.
It is hard to shoehorn thinking NPCs into 6 encounters. I'm running Emerald Tower right now, and the first two levels are just filled full of lazy, incompetent or unintelligent enemies that are barely capable of working together. If they were men instead of goblins, they would blow a horn and fight you all at once.