'src' has inertia carried over from Unix. Unix systems have kept the source is /usr/src since since at least the late 70s. That's in keeping with the general terseness of Unix. Similar to how only errors are reported; successful execution means nothing is printed by default but a new prompt. And it's why most of the original file system manipulation and text editing commands are 2 or 3 letters long. Tradition now, I guess.

Originally, way, way back in the day, there was good reason to be so terse. The first UNIX machines had literal teletypes for terminals; printers with moving parts. Every extra character meant wear and tear, paper, ink, and especially, time.