No matter how unique NPCs patterns are, they will eventually get "old" to look at overtime. and giving npcs patterns to follow ( and not just one were talking like 50+ npcs per city). That's a pretty hefty coding job with that alone.

As long as they "pretend" to have a conversation with another NPC ( for years and years XD haha) Or Tom NPC walks to Store gets food, then walks back to stump to eat his food, only to walk back to the same store to buy the same food, and eat it at the same place again ( for years and years to come XD). Then I wouldn't mind NPC be "Lively".