The first programs were written in binary/hexadecimal, and only later did we invent coding languages to convert between human readable code and binary machine code.
So why can’t we just do the same thing in reverse? I hear a lot about devices from audio streaming to footware rendered useless by abandonware. Couldn’t a very smart person (or AI) just take the existing program and turn it into code?
Computer code is very complicated, so when humans write code we write in a way we can understand. We name functions and variables with names that make sense, and we put comments in the code so we can understand how it works.
Compliers don’t care about any of those things. Variable names are turned into numbers, and comments are ignored.
You can convert machine code back to source code, it will be missing all those human readable labels and explanations. You can recreate them, but its a major process. Reverse engineering is done sometimes, but there’s a reason is not common.
There’s also the issue of licensing. An important part of free and/or open source software is that you have permission to modify the source code. You probably don’t have a license to use the code if its closed source. There are ways to do this legally but it adds extra hurdles and inconvenience to an already major process.