Backdoor is not what is not mentioned today but it is what will be sought when Apple does make an unbreakable phone.

If a loudly media backed ruling to force Apple to comply with the FBI is then followed by Apple making a phone which makes it impossible to comply with such requests in the future, it will much easier to get legislation or rulings requiring the all phones have an inbuilt backdoor.

This is why the FBI is forcing Apple specifically to do what they or another organization (eg McAfee) might do. Especially since the phone in question, while spectacular from a media perspective, probably has very little interesting on it.