to do that, apple would have to create a key that opens ALL of their phones and give it to the FBI. do YOU want the FBI to have that kind of key for ALL iphones? do YOU believe, for even a second, that the FBI wouldn't use that key ANY TIME they wanted to in order to search a phone?
It's more than just creating a key.
The FBI is actually seeking a weakened version of iOS be developed for them to use, ostensibly, on this one phone.
As I'd noted earlier, I don't think anyone believes the FBI wouldn't immediately get into that newly-developed iOS and use it ad voluntatem.