The short answer is that Mojang doesn't care about implementing actual, innovative features.
The long answer is that the game is in a managed decline. The target audience is small children so anything not targeted to them doesn't get implemented. "Smart NPCs" isn't a feature like that, so there is zero chance of that being included into the game.
The long answer is that the game is in a managed decline. The target audience is small children so anything not targeted to them doesn't get implemented. "Smart NPCs" isn't a feature like that, so there is zero chance of that being included into the game.