That is one of my biggest pet peeves.
I even yelled at the TV last night when Tim Allen did it on Last Man Standing with a 1911. Not sure how much he knows about guns, but he seemed very comfortable when he sat down at his desk and popped the mag out and set it down.
I drill that in during my CHL classes, we talk about it in class and lots of guys laugh and say they would never do that. Then when we go to the range, I am yelling "Index, INDEX INDEX" till everyone gets their finger off the trigger. After the second time I'll call names so everyone knows who keeps holding up the show. I won't let them start a string till they are all indexed.
Funny thing is, the guys that laughed about it in class are the same ones that do it on the range.
I figured out a long time ago that it is likely caused by bad muscle memory created when we were little boys running around all day shooting at each other with water pistols and cap guns. We have hundreds if not thousands of hours logged in running around like that without anyone correcting us. It takes great effort to create a "new" (to some) muscle memory of staying off of it.
I know guys that will do it with an empty gun and when I bitch they get irritated and say "It's EMPTY".
It's a battle.
Thanks for pointing them out. We'll have to wait and see if we hear of a ND on the show.

Carry safe and carry when and where you can. I'm just sayin'.