Ill assume some instructors do not teach neutral buoyancy in OW class because it is not a requirement and they are in a hurry or just assume the divers will learn it on their own. Maybe it is because some instructors never really learned it themselves
For a friend of mine it began for her when she went for her OW checkout dive and had to put on a wetsuit for the first time.
she "could not" get under so the instructors just kept putting on more weight. so on her first uncontrolled OW dive without an instructor she just assumed she needed 26# to get down.
had the instructor taken the time to make sure she did not have any air in her BC, and that she shook off the air bubbles from her new wetsuit, or better yet required the students to wear a wetsuit in the pool, then maybe she would have known 20 dives earlier that she only needed 12#.
think of all the OW students that are taking their course because they plan to dive for the first time on a beautiful undamaged reef. and the instructors are basically sending ballistic missiles to go blow the reef up. Maybe that is harsh, maybe it is just realistic.