Because the cooper rules are UNSAFE.
ROFL!!!!
I've asked you to actually show that supposed "research" several times, over the years, and have so far seen exactly NOTHING from you.
I think you misunderstand Jeff Cooper's rules.
Rule #1 ("Guns are always loaded") generally gets tossed around without background explanation, and can be interpreted to mean "Always keep your gun loaded at all times".
This is not what Cooper meant. I've read his book. What he meant was that one should always assume that a particular gun is loaded until you have personally verified that the chamber is empty and there is no magazine inserted. Even then, if you put the gun down for any reason, when you pick it up again the first thing you do is re-verify its unloaded condition.
A major cause of firearms accidents is the gun-holder being sure that the gun is unloaded, and pointing it at a human (or at a wall which a human may be behind) and pulling the trigger. Then he gets to find out that his assumption was invalid.
Cooper is also talking to a different audience than the audience the NRA rules are primarily for. The NRA rules are great rules for pistol target shooters on the range, who arrive with an unloaded gun, shoot, and then unload the gun to go home. Coopers rules are for people who carry guns off the range (CCW) or who for defensive purposes may keep loaded guns in the home.