How is it different than getting a phone company to install a wire tap?
What you describe is not what's being asked for. What the FBI wants is a tool to get into this phone. They will definitely want to get into more phones in the future, but that's not the same as a single tool that gets into any phone. It can be a new one every time. If it wasn't possible to make such a tool, I'd be a lot more outraged. But it is. Tell me why that can't be done.