It's not available to everyone--for example, a lot of institutions don't have wireless (lol) and have pretty strict controls on devices that plug into the wired networks.
what if I break in to the network through a web server? or happen to find an open network port in my hospital room?
Security is done in layers. Physical access is 1 layer, network security is another, requiring proper authentication/authorization for your software is yet another, etc. Each layer stops a percentage of hackers. If you skip important layers like auth, you're allowing a larger number of people in, simple as that.
It's the equivalent of saying "but ofcourse I leave a large pile of cash in the middle of my dining room, my front door is locked, that's secure, right? Putting it in a safe or even a locked closet is just a burden." It ignores basic security principles.
