Oh I don't know about that. I briefly joined a Pathfinder 2 group that was doing Age of Ashes. It was brutal! We were on the edge of a TPK with nearly every combat.I think it's because "by the book" the encounter should be balanced and winnable - at least based on the guidelines of the system. Or you figure that if the party is outmatched, that they will be able to regroup or change tactics. And sometimes you do want tougher encounters, but it's hard when as a DM you describe a single skeleton and it sounds terrible and frightening, but the 3rd level ogre doesn't sound as terrible. And how do you convey that to the players? Do you tell them - "hey, this ogre is a potentially deadly encounter" and "this skeleton is a trivial fight."
Now, two of the other players were playing casters, and they relied on just a couple of their spells, over and over. They didn't even know all their spells by name, much less what the spells actually did! The melee players were a little more on the ball, but even they weren't always doing the PF2-optimal thing. (PF2 really is a different beastie than 5e.)
Even so, I did follow Pathfinder 2 forums during that time, and that adventure path had a...reputation. So I would not just trust that any published adventure path is balanced and winnable. The adventure could be really tough, or the players could be, shall we say, sub-par.
Edit: Fixed a typo.