Well, of course it's about the evidence. I doubt they just like to crack into phones for the fun of it. The point is WHICH evidence was the primary reason... the data on that phone, or more broad access to data on any phone they might target.
The worst part in all of this? The broad brush that was used by the FBI that unfortunately paints some really great agents out there with a negative view as seen by the public.The term FBI has become something far less than it was.
Unfortunately, that's pretty much the whole of the government anymore. Yes, there are some good people working within it, but as an institution, it's now so corrupt as to become the 'bad guy.' (Or, at least in these kind of sweeping ways, needs to be viewed and treated as such.)
As I've mentioned in other posts, if you have even an ounce of trust for the government any longer, just listen to a podcast called Congressional Dish. The host goes over what is happening in Congress... stuff like watching the hearings and reading the bills. I don't even always agree with her political slant on things (i.e.: what stuff they are doing that she thinks are good/bad), but it *quickly* becomes clear that these people aren't representing us. What they are actually doing makes some of the conspiracy theories pale... and it's being done right out in the open! (ex: the CISA stuff they stuffed into the end of the last budget that was railroaded though, which most of the Congress-people didn't even read.)
I'm with one of the responses above. I think it got a bit too hot to handle, and they were instructed to back off.