Because a lot of the folks who edited the silent films and added sound effects had never been around such and assumed based on the visual.
And as far as movies, to me, there are three types of flicks - those I hate the subject and story line and can't bring myself to enjoy or suffer through even if I try; those that I can suspend belief for 90 minutes or so and enjoy the story even if the details are lacking; and those where the technical aspects are correct to the point where they bolster even a less than perfect story line. Certain directors who insist on technical accuracy and excellence and will even change the script and veto the writer's golden words when they don't reflect plausible reality are rare. Much more common are the ones who disrespect the intelligence of their audience so much that it doesn't matter how ridiculous the technical aspects are. Even if it could only happen in a comic book or by suspending the laws of physics - they'll go for the shot.