You're perfectly welcome to keep your computer and its software running in isolation until the end of time or until the hardware fails. You just shouldn't expect to be able to connect to networks that change over time or to run software on new operating systems that address newly discovered security vulnerabilities or that otherwise get updated.
Networks don't change over time. Centralized "application-servers" do. Making applications network-dependent when they don't need to be is a part of the problem.
Security vulnerabilities don't change OS APIs. OS APIs are one of the most stable constructs in computing.
There is a huge subset of software that doesn't require interaction over the network, and can be written to last. And even inherently network-dependent applications could be written using p2p technologies, making them independent on anyone's computer. Just because the everything sucks right now doesn't mean it has to.
