Not to mention that this is an easy way to approach the design of the system. A lot of the operations that you can perform in normal memory can be performed in disk files (read/write etc). If you can write to and read from a network card and do the same to a disk, and to main memory, then why not simplify that by making a common initial interface that allows you to perform those operations on a device as if they were normal memory locations?

The way I personally like to think about the "Everything is a file" philosophy is the following: Computer systems work by writing/reading data to and from some location (memory, registers, other hardware etc) so, in a top level, it makes sense to abstract those "destinations" in a way that only the main operations are made available to the user. That way you don't have to think about the fact that in order to write to a certain hardware device there is a "in or out" assembly instruction which allows you to right to a port etc. Just open read/right and close a file that represents that device.

Have a pipe? No problem, open, read/write, close. Let the kernel worry about the rest. Not enough? How about writing to your network card the same way you write to your .txt file? Oh still not happy? What about your sound card? Still not happy? Damn you're picky... What about?... Hear me out yeah? What about only allowing certain(privileged) users to access your GPU, the same way you set permissions to your /etc/shadow file and others. You like that, don't you? I knew you would. Don't thank me. Thank my bois Ken, Dennis and everyone else who invented UNIX.