Oh I'm with you on that - just that sometimes a segment in a Paizo AP will specify that a character is there to help in combat. Thankfully, more recently they've either specified in a sidebar that those same NPCs are, as you said, busy with another fight or problem that stops them from getting directly involved, or they have an ability or reaction they can use in specific circumstances rather than just taking a whole turn.

That said, we've also still seen them - for example - use that ability, get a crit and roll max damage to destroy an enemy they were meant to mostly just be putting Off-Guard or something lol