alt Hacker NewsA decompilation is not clean room, nor is it "created from scratch". If that was the case, you could just compile a program to remove the copyright, because the machine code doesn't resemble the source code at all either.
A reimplementation or a behavior-based clone is an entirely different legal world from decompilation.
The compiled binary is protected and the property of the original company. The source code written by people doing decompilation is owned by the people doing the decompilation. That source code can compile to a lot of different binary representations, just like a lot of code representations (infinitely many) could compile to the original binary.
In fact, the goal of most decomp not to produce the same binary, that’s just used as a validation.