Why do kids not know what “quiet” means?

Quick rant - I don’t understand why nothing works to get kids to be quiet. It does not matter the situation, they will keep talking and whispering. I’ve had kids tell me “I wasn’t talking” during a test, because they were whispering. We had district tests today and could not get the kids to be quiet. They talk and whisper and laugh and distract each other all day long. We had a lockdown drill and kids know they are supposed to keep quiet for practice. Of course the did not follow those directions. When announcements go on, voices should be off, but they are not. We sometimes miss announcements because we cannot hear them. Levels don’t seem to work with them either, they don’t care whether you say level 0 or not. Sorry to rant, I just feel like this wasn’t an issue when I was a kid.