Why aren't turrets built out of the same material as walls?

Not equal makes sense. A hundred times as good does not.

Is there any particular reason a wall needs as much health as it does? Not really. Walls were never good at blocking enemy movement anyway. Its best use is to act as a health multiplier for defensive turrets.

A short wall blocks movement. A tall wall blocks bullets. One contradicts the use of the other. That's why dragon's teeth were SHORT.