Okay, let's unpack this.
First, though some gun carriers may watch too much tv (and so think they are going to take out the bad guys, get the girl, go to commercial), mostly they will look to get themselves and their companions to safety, just like the rest of us. That's the smart thing to do.
Second, gun carriers are at a decided disadvantage against someone who goes into a school, or store, or crowd, and starts shooting everyone. While the shooter doesn't discriminate in his targets, the legal carrier will (and should). When hysterical people are fleeing in every direction, when echoes make it hard to determine how many shooters there are and where they are, when other gun carriers may be doing what you are doing (and you don't want to shoot them, right?), it makes for an untenable situation.
Third, most people just don't want to carry a gun.