Actually they always do, if we have a right to something it was already there before the ruling. Just as executive immunity was always there, they simply defined it. They take up cases when the courts are in conflict as to what to rule and they define things, it is their job.
Such immunity has been exercised by many different executive offices, just as I described (and even stated I do not like). There is nothing new here, it has simply been defined, just as before they ruled on the DAs I talked about earlier the same immunity applied to them... it was defined by the SCOTUS (much earlier than this SCOTUS).
While I sometimes disagree with the ruling, there is nothing at all new in this one.