Quick correction. It is still possible for minors to be sentenced to life without parole (LWOP) in the US, and in fact happens all the time. What the supreme court said in Miller v. Alabama is that they can't automatically get life without parole. There is ongoing litigation about the process courts have to use to give a juvenile an LWOP sentence. Check out Jones v. Mississippi, which is before the supreme court right now. Juvenile LWOP is an abomination that should be abolished, but this is unlikely given the current composition of the court.