They tested using a green light for the front brake light, not a red one

I don’t think it’s accurate to say that everyone can just decompile the code and reuse it. Decompiling and reverse engineering a binary is incredibly hard. Even if you do that there are some aspects of the original code which get optimised out in the compiler and can’t be reproduced from just the binary.

The GPL uses copyright because it’s the legal mechanism available to enforce the principles that the GPL wants to enforce. It’s entirely consistent to believe that copyright shouldn’t exist while also believing that a law should exist to allow/enforce the principles of the GPL.