Can somebody explain what's going on here? It seems I'm missing some important piece of background info. Why don't they just add -J flag for everyone who wants

Can somebody explain what's going on here? It seems I'm missing some important piece of background info. Why don't they just add -J flag for everyone who wants to output JSON? Oh, wait, tree already has -J flag to output JSON. So WTF are they doing here? I am especially confused by this: > Surely, nothing will happen if I just assume that the existence of a specific file descriptor implies something, as nobody is crazy or stupid enough to hardcode such a thing? Wait, what? But "you" (tree authors) just hardcoded such a thing. Do "you" have some special permission to do this nonsense?