Because code still would be read by humans. Check the code for PhotoCraft[0] (clean room reimplementation of Adobe Photoshop) which is being actively written in Rust by AI agents almost 24x7.

Check the overall layered architecture. That's nowhere AI. That's pure human ingenuity coupled with machine's raw horsepower to build on top.

And such people do need to read the code.

[0]. https://github.com/storytold/photocraft