Every package manager I know of lets you install a package directly without any kind of Internet connection (I haven't tried much, but I've run into CORS errors with file URIs that suggest browser authors don't want those to work). They also--critically--allow you to not update your software.

The web today is mostly a media consumption platform. Applications for people who want to use their computer as a tool rather than a toy don't fit the model of "connect to some URL and hope your tools are still there".