SCOTUS has already ruled that the death penalty is not cruel and unusual punishment - more specifically, that since it is not unusual, it is not a Constitutional violation despite where you feel it falls on the cruelty spectrum. A common pleas or even circuit court judge can't simply say "lol whatever I'm going to ignore that." Only SCOTUS can reverse its position on the Constitutionality of the death penalty.
Your substitution is inaccurate. The rulings effectively mean that the death penalty is cruel and unusual except in certain, very specific circumstances. Only the most extreme crimes qualify. Even the rape of a child is not extreme enough unless done multiple times. It might seem applicable to only a few cases, but that is only because few states attempt to apply the death penalty except in the most extreme circumstances.
A lower level court judge can make a ruling, like finding a $250 fine for a poor person cruel, that stands, because it's not a SCOTUS issue. The death penatly sure, and the legality of it has already been decided in the U.S., and is usually for serious crimes. But for low-level offenses, the likes of which are rarely — or basically never — brought before SCOTUS or higher level courts, a judge can rule in any way he sees fair, as that's his job.
Of course the states are free to outlaw the death penalty, that doesn't address whether or not it is Constitutional. There are plenty of things that are completely Constitutional but which are outlawed in the majority of states.
As far as popularity goes though, the death penalty has been more popular than not for all but a brief time in the 60's[0], and I think it's dangerous to conflate popularity with Constitutionality, or to suggest even implicitly that they should have any bearing on each other.
But SCOTUS can only reverse what is brought to it, right ? So a circuit court judge has to ignore that so that SCOTUS can have the occasion to reverse its position ?