Because actors and producers have realized they don't know enough to handle guns safely and have hired experts to do so for them. There are people who's entire job is to make sure the guns are safe, they take on that responsibility so the actors don't have to. Cordex described it pretty well earlier in the thread.
I think it's time for this to end.
I also don't think it ever existed in a more grossly incompetent and negligent environment than today when it comes to firearms proficiency.
Does anyone think Gary Cooper, John Wayne, or Clint Eastwood were as ignorant on firearms knowledge as someone like Sean Penn or Alec Baldwin? Those 3 actors were prolific in films with guns, fired hundreds or even thousands of shots on camera, and I'm not aware of firearms related injury or homicide on one of those sets. I'm sure there was plenty of actual plinking with live rounds that even happened between takes or to get into character or build skill and familiarity with the set weaponry.
Look at Keanu Reeves, particularly in regards to the John Wick franchise, and his extensive training he undergoes with 3-gun coaches and such while getting ready to film. I would be shocked if Mr. Reeves didn't personally inspect his weapons and ammunition carefully when handed to him, to confirm his prop is indeed in a condition he's personally prepared to accept the consequences of his trigger presses.
Actors who are ignorant of firearms safety and go out of their way to make firearms knowledge a taboo or difficult to obtain, should be distrusted to participate in films that involve firearms use.
Were I an actor and issued a weapon by the propmaster/armorer and told to shoot at at the camera (with a squad of technicians behind it to record everything), you can be damn sure I'm going to eject every cartridge from the system, inspect them, look the weapon over to see if it's functional or not (plugged barrel? nonfunctional firing pin? etc) and if I'm told to trust the blanks then I'm going to ask for a new unopened box, and go discharge some of them at a safe backstop and inspect for downrange particles (i.e. shoot at a sheet of paper at 10 feet, 25 feet, etc). Then use the box I've personally seen to be "safe" and keep it and the weapon under joint supervision of me and the armorer, until I need it on scene. Discharging anything in the direction of another person absent legitimate violent intent is too dangerous for anything less than personal accountability and ownership.
Have you guys all seen Penn and Teller's magic bullet trick? Where one shoots a .38 special revolver through a glass backstop, and the other appears to catch it in his mouth? Real guns, real projectiles. Not quite as it seems and there is illusion going on here, most likely with deliberately mis-aligned laser sights causing them to shoot offstage rather than at each other, and slight of hand while donning protective gear. But it's a live on-stage discharge of a .38 special cartridge with projectile. These guys meticulously own their weapons used and take ownership of the actions done with them while entertaining an audience. They're actors/entertainers, but they know very well what they are about when using those weapons. If they can do it, then Alec Baldwin can bother to learn enough to determine the load status of an SAA.
Abdication of responsibility, when using a REAL gun, is just abhorrent. I don't care if you hire police or military armorers or whatever to supervise. No one can take away ownership of pulling the trigger.