Pretty much any question about why things are done a particular way in Unix can be answered the same way: "for historical reasons".
I'm a full-time Linux user, so that's not intended as a dig against Unix, but merely an observation. Each of the traditional Unix utilities evolved from some earlier tool, and carries with it to this day both the quirks of its predecessors and many artifacts of the design constraints of the time. Some argue that this diminishes usability, and they may have a point. But I find that it gives Unix a certain charming character that I've grown quite fond of. I suspect this sentiment is fairly pervasive, and probably contributes substantially to Unix's resistance to change over time. Maybe it isn't the simplest thing to learn from scratch, but it's robust and highly dependable once you've learned it.
I'm a full-time Linux user, so that's not intended as a dig against Unix, but merely an observation. Each of the traditional Unix utilities evolved from some earlier tool, and carries with it to this day both the quirks of its predecessors and many artifacts of the design constraints of the time. Some argue that this diminishes usability, and they may have a point. But I find that it gives Unix a certain charming character that I've grown quite fond of. I suspect this sentiment is fairly pervasive, and probably contributes substantially to Unix's resistance to change over time. Maybe it isn't the simplest thing to learn from scratch, but it's robust and highly dependable once you've learned it.