That pretty much says it IS a thing in real life. It may not be supposed to be there, but it does appear in real life.
code will allow you tie someything flammable to a duct that would be heated and can catch it on fire
... how hot do you think the air coming out of a duct is? Also, this isn't a discussion about what codes allow, this is about what happens in practice.
they would ONLY be used while the techs were actively diagnosing a persistent issue
I've personally seen them placed by people who were having issues with building management messing up the hvac schedule, and I'm sure there are other cases where they would be used. You're extrapolating your one use case to everything else.
Why do people perpetuate obvious fake Hollywood stuff
All I said was, there's a real life basis for the trope. And there is, even you've admitted to it. So I'm not sure what your big argument is about...