Because people are only as smart or dumb as the plot needs them to be.
Or like cops. If i walk out on the porch and fire my glock 29 3 times I'll bet you my bank account that the cops show up within minutes ....but on TV you can blast off with a machine gun for 5 minutes and the cops only show up if the plot needs them to.
It's hard to watch movies and TV if your brain is still switched on. I notice all kinds of nonsense. Characters logic and intelligence, all kinds of gun stuff and everything about cops sticks out to me.
Ever watch law and order sv ? Eliot Stabler would probably be in jail , cost the city a fortune and likely would have had his convictions overturned due to his conduct. At absolute minimum the dude would have lost his badge at some point