Well, let me test my memory. At one time I was well read on this subject.

To the question about why some have external safeties and some do not -- the professional answer is:
“there is a market for pistols with external safeties and a market for pistols with no external safeties.

The glock style trigger safety and the S&W trigger hinge safety are both primarily anti drop safeties. When someone drops the pistol the inertia generated when it hit’s the ground will not move the trigger bar inside the pistol.

The old 1911 .45 auto workhorse was perfect for two world wars. In the 1960s (as they were gearing up for the series 70?) I read a well written article. The writer claimed (and I believe) that the inertia firing pin can not fire a cartridge unless dropped from a building about ten stories high onto cement with it landing perfectly on the muzzle. Assuming the force did not push the slide back enough to activate the original out of battery slide lock.

I have not looked closely at the new 1911 style 45 autos but the inertia firing pin does not reach from hammer to primer at the same time on any I have seen. It must travel forward of its own inertia to pop the primer. If you have time some day take a tongue depressor or similar wood and push down a 1911 45 firing pin level with the keeper, then notice it is not sticking out the of the breach face. The safest way to carry a 1911 45 auto is hammer down with loaded chamber. Second safest no doubt is cocked with leather strap under hammer over firing pin. (People who have gun accidents can be creative in ways to blame the gun). (Therefore the suits in the front office that order guns for police and military love lots of safeties).

The S&W model 10 revolver we all loved probably had a 12 pound double action trigger pull and a 3 or 3.5 pound short crisp pull for accurate shooting. It was the perfect police handgun like the 45 auto was the perfect military handgun.

When the big city drug gangs got more and more firepower the police had to keep up. When Glock first came out with a polymer frame, striker fired, half cocked gun with high capacity magazine it was wonderful. I believe my first Glock 17 has a 3.5 pound trigger. Apparently many accidents happened when they were shoved in behind a belt with no holster and also with the overly flexible inside the belt holsters. A few accidents happened when officers crammed their gun in holster after an incident with finger still on the trigger. And many more.

Anyway it seems to me that Glock and S&W and Ruger have jumped up and down on trigger pull poundage trying to make everyone happy. I believe my gen 4 glock in 40 caliber has a 6.5 pound trigger (again if memory serves). I believe my Ruger P95 is a couple pounds higher but longer and smoother.

I believe the original New York (police) Trigger was 9 pounds. The police buyers are feeling around for a compromise between the revolver double action trigger and the cocked single action revolver trigger.

When I was in the Navy in 1960 a marine at the gate playing quick draw accidentally killed the marine coming to relieve him. The chamber of his pistol was supposed to be empty and he was supposed to not be playing with it.

After a police gunfight is over one must holster ones weapon at some point. Most European style decockers are loud and uncomfortable. Dropping an exposed hammer can be done quietly with practice. Pull the hammer back slightly with finger off the trigger. Push down the decocker levers and lower the hammer. But if one gets nervous there is a chance one could have excessive bump or pull on trigger before decocking and the slide will come back and bust your thumb. So you just push down the decocker and let the hammer slam down and watch everyone around you jump perhaps?

Lets talk excessive safeties. I have heard of police riot holsters with three locks to prevent someone getting control of your gun. So perhaps a couple thugs are stabbing you or shooting at you and you must first hit the thumb paddle safety on the holster while poking finger inside trigger guard and whatever else. Then you get the gun out and must push down the thumb safety on the gun.
A friend of a friend would approach cars with his clipboard under his left arm and left hand in jacket pocket on his pocket mauser already pointed at them.
A minority officer who was interviewed walking home in New York clearly stated “in my neighborhood you do not have time to draw, so you take your pistol out of the holster and put it in your coat pocket.
(this is getting too long - bye)