And, contrary to your description, that power is expressly not a power limiting it only to “determine constitutionality, and interpret existing legislation” whereas trial judges have “huge amounts of discretion in making their judgements” that the Supreme Court lacks (in fact, as the Supreme Court has, but rarely exercises, appellate power over fact decisions as well as law, its domain is broader, in jury trials, than that of the trial judge, who is the original trier of law but not fact.)