The same reason I didn't learn woodworking, even though my house is mostly made of wood.

I mean, look, I'm a professional C/C++ developer, and have been for 30 years. But the fact that your tools are written in it doesn't mean that you need to know it. (I need to know it because I work in embedded systems; C/C++ is the language of choice there, even now.)

You realize that computers don't literally run C code, don't you? By that argument you should go further and build your own hardware, then write your own OS...you get the point.