It's because, due to how ratings are determined, you are limited in how you use the word "fuck". You can't say something like "We should fuck" or "And then we fucked" because that would be "too sexual". You also can't use it as a direct insult and say something like "You're fucking stupid".

You could probably get away with something like "We're fucked" because it's general enough. You could also do just a general "Fuck" in response to something bad happening.

So "Open the fucking door" works because it is directed at the door, which is fine.

*(Note, film ratings are mostly made up. If you're a big studio with a big film you can probably negotiate to use fuck however you want.)