OK, back to the OP. The point is, no agency actually tells you to overweight your students. There are those instructors who find it easy to keep track of their students if they turn them into rocks. Bad idea, and it means the instructor is both lazy and a pitiful instructor. But don't blame the agency for That happening. Blame the instructor.
Then you have the vacation spots and DM's and Instructors who find it easier to keep track of rocks than the wavery once a year vacation diver that they run across. They identify them as such because those divers don't remember how much weight they use where in what conditions and they let the DM figure it out. That busy DM usually is not going to burn time doing a hundred buoyancy checks... I didn't say it was right, just usually the reason for vast overweighting...
I teach skills from a fin pivot and then only from a hover from the first pool session. A diver doing skills on his/her knees is pointless for them and lazy for the instructor. In my opinion...