Have I fundamentally missed something between the time when I sat with my 486 IBM PC in the house, fully offline, and today? Do normal people actually set up complex local networks in their homes where they have some kind of "trust anyone with an internal IP address" security scheme going on?

What does "gaining access" to a home network mean? Is that, like, exploiting the NAT router (if such a thing is used, which has not always been the case for me)? Even if they exploit the router, that doesn't magically give them any "access" to the "network" (meaning PCs connected to the router)? At best, they can maybe read plaintext traffic, but how much such is there these days? I shall hope 0% of all traffic.

So what do people mean when they talk about "gaining access"? No updated version of Windows has ever just allowed somebody to randomly connect remotely to "gain access", regardless of the presence/absence of a router/switch/whatever in between. Or, if it has, that's some kind of "0-day" exploit or unknown-to-the-public exploit. The so-called "hackers" that people talk about more than likely never "gain access" like that at all; I bet it's 100% social engineering and tricking them into running coolgame.exe as sent to them in an e-mail attachment and things like that.

My intention with this question is to understand people and the world. I'm genuinely wondering about this since not a day goes by without me feeling extremely paranoid about security and privacy, especially knowing how incredibly naive I used to be, and how naive people in general seem to perpetually be about these things.