Perhaps because the very reason why you always should dry-fire a weapon while clearing it is to make sure it really is not loaded.
So, you're saying to confirm that your check of a weapon was actually correct, and that it is clear, that the thing to do is pull the trigger, the one function that will actually discharge a round if your initial check was wrong? This sort of defeats the purpose and definition of "make sure it really isn't loaded" for safety purposes, don't you think?
The reason that pointing in a safe direction after confirming a weapon is clear and de-cocking or dry firing is to put the firing mechanism into an "at rest" state for purposes of keeping said mechanism, springs, and other stressed and wearing parts into a state that puts the least stress on them if it is being stored, but primarily it serves as a safety feature - avisual aid in the case of weapons with exposed hammers, so that it is readily apparent to anyone looking at it that it that the hammer is down and in a safer condition that being cocked. Example, a 1911 that has been cleared and re-holstered on a range or during a course that still has the hammer back will attract the attention of wrath of the instructor or even other students, as it would be "hammer down" if the proper procedure on the line was followed - remove magazine, visually and tactily verify clear, release action/slide, decock/release hammer/dry fire in safe direction, the re-holster. In the case of DA/SA/Internal Striker pistols, decocking or dry firing in order to accomplish the same thing is done for consistency reasons in terms of reholstering or storing the pistol after it has been cleared as well. It has NOTHING to do with "verifying" or "confirming" that your visual and tactile check that the weapon is unloaded was right the first time, as if it wasn't, and you do dry fire it, the obvious result is "bang". Kind of purpose defeating in terms of "making sure it's unloaded" don't you think?
Only a very few guns are made with a decocking feature that does not require the trigger to be depressed. I've personally never held such a weapon
I don't understand what you're saying here G. I think there are MANY pistols that have de-cockers where you do NOT press the trigger to engage them. The Sig 226, 220, 229, 228, CZ75/85/ BD models, CZ SP-01 (D means decocker), Most of the Ruger DA/SA line, HK USP, HK45, HK2000, Beretta 92/96 have a decocker built into the safety switch as well, the Walther P99's we ran on our range also had a decocking device, on the top rear left of the slide activated by the right thumb, it put the internal striker into it's double action stage with the longer pull, some of the Smith semi auto's have decockers as well, many of the Israeli "Baby Eagles" and "Jerichos" are decocker models.....you get my drift. A majority of combat double action/single action pistols have a decocking device included, so pressing the trigger isn't necessary. Ever try to pull the trigger and release the hammer slowly with your thumb when your hands are frozen from shooting outside in -40 or colder weather, or when you have blood, or sweat, or even just wetness from the rain on your hands? Decocking is far safer and more reliable for putting your pistol into a re-holster safe condition.
I would also like to say that most, as in a huge majority of accidents that good or experienced shooters have is related to dry firing after failing to clear the weapon properly due to either distraction or being overtired, or just plain making a dumb mistake and not following all the rules in the proper sequence. Dry firing in of itself is a very important tool for shooters, I was taught, and nearly every reputable gunfighting school teaches, that 80% of your training and practice with a pistol should be dry firing at targets, and running through your drills dry. This allows you to build and improve your fire control (trigger press) skills far more quickly and cheaply than with live rounds, and also allows you to train any place you like that gives you some privacy, without having to go to a range.
As far as the OP and firearms safety, verifying that the weapon is clear is obviously the most important thing in safety, pointing in a safe direction, removing the magazine, visually checking the chamber and magazine well for ammunition or any obstructions at all while KEEPING the weapon pointed in that safe direction, then repeating the process with the index finger of the non dominant hand, in order to have a tactile confirmation of the empty status (this is not just a brain teaser type of thing or a confirmation, it is done to simulate having to clear a weapon in low or no light conditions), then release the action/slide, decock/dry fire/hammer release, then re holster, or re store.
Another very important thing regarding safety is weapon handling while using it. We teach that you should imagine your muzzle has a constant beam or laser coming out of it, and anything that beam comes into contact with will be destroyed. In other words, if you need to turn/move in order to engage or point your weapon, be cognizant of the things and obstacles in the path your muzzle will take. Example, if there is a friendly ten feet in front of you, and you have to sweep through him in order to move or point your weapon at something to the other side of him, you need to lower the muzzle as you trace the path AROUND AND BELOW him before bringing your weapon back up to engage your target. There are many different examples and cases of this, but the bottom line is you move your body and weapon muzzle AROUND friendlies, and NEVER sweep them with your muzzle.
One last point, is that your fire control/trigger finger is an important factor as well. That finger only goes to the trigger when the decision to fire is made, and then immediately returns to its off the trigger posture when done firing, and scanning using universal cover techniques, or whatever way you've been trained to follow through after firing/engaging. If you watch any of the MagPul training videos on uTube, they show a good example of this with the AR platform rifles. The instant the shooter is done firing, then scanning, the safety is immediately engaged on the rifle. Then, when a new target is engaged, the weapon comes up and presents to the target, sight picture acquired, safety moved to the fire mode, finger then moves to the trigger, presses it, finger comes off the trigger and returns to at rest spot on the receiver, scans are done, then rifle is put back on safe. It sounds like a lot to do in order to just shoot something, but it can all be done VERY quickly, and is critical for having consistent safety both operationally and on the practice/training range.