SIC is a gigantic party, and everyone is invited. They're all in one massive dome together, but just because they're at the same party doesn't mean they're talking to everyone at the same time unless they're specifically pausing to speak to the entire party as a whole. But just because you're at the party, it doesn't mean that the announcement made is about you, or even anything you care about, so you can just choose to ignore it.
There are hundreds of conversations of all topics, types, shapes and forms, the constant and connected thought of millions of people shorn down into relevancy. The only reason you 'hear' what you hear is because either because it's relevant to you in some way, or you just happened to hear it at that time.
Imagine a group of people are talking at this big party. There are millions of these groups out there, but you're near this one. Why do you engage? Because you overheard something that either interests you, or you know one of the people talking in the group. You can choose to engage or not engage, and sometimes staying quiet and just listening is the best option, but what you hear is just what you hear, because you're near just one of these many, many groups of people at this massive, massive party. Some person in the dome, may hear something else entirely different over SIC.
The playerbase, as well as some of the NPC base, are in this group, 'this' group. Sure, you can yell out an announcement to the whole party (the entire city), but it doesn't mean they're going to hear you or care, no matter who you are.
I hope I'm making sense and not just making it more complicated.