There’s no one answer for everything.
Movies do a lot of great things. In the course of two hours they paint a great and colorful landscape of action, scenery, and emotions. But still, only two hours. About the length of four anime episodes. And on top of that, when dealing with fantasy and science fiction, Hollywood has gone for the big, flashy, and showy. Especially when this lets them pit a lone Hero or few against the Dark Forces of… whatever. Which means they simplify things.
One of the classic examples of this being werewolves, and the silver bullet.
What’s interesting about that is it’s genuine werewolf lore, but it only goes back to about the late 1700s – Wikipedia speculates the Beast of Gévaudan as the source of the lore, and that would make sense, given the creature was supposed to be demonic, and silver has been considered holy for a very long time. (There’s also earlier bits on using silver against shape-shifters, not necessarily by way of bullets.)
Werewolf lore, however, goes way, way back, possibly as far back as Proto-Indo-European mythology and definitely as far as ancient Greece – see Lycaon, but mind that story is gruesome. And while people back then may have had silver, they definitely didn’t have bullets.
…Not that they would have thought they needed even silver, most of the time. Up until the Beast, it was pretty much assumed that a werewolf was just as prone to normal injury as any wolf, and one of the ways to identify them was to find a human with the same injury as the wolf had taken. And a werewolf was not always a werewolf forever. Some people were cursed for a certain number of years; some cases could be cured by exhausting the afflicted individual. In fact, in some times and places, addressing a werewolf by its Christian name would not only stop it from attacking you, it’d cure the werewolf.
I suspect this is just not dramatic enough for Hollywood. Which is a darn shame. Can you imagine the possibilities for a tense thriller as a detective tries to deduce who the werewolf must be, so they can shout the name at the next attack and stop the whole monstrous plague in its tracks?
And yes, this goes along with the whole “tired of saving the world” post. Because honestly, Hollywood werewolves ought to have taken over the whole planet pre-bullets ever being invented. For werewolves to make sense, small-scale heroes have to be able to fight them!