>the "why" of the verdict
SCOTUS doesn't have "verdict[s]".
I'm not a lawyer but I've read probably 200+ opinions for fun over the last decade, listened to maybe 100+ oral arguments. I really love following the Court, and I probably have an allergic reaction to these people growing beyond their britches (they are unelected, after all).
Both conveniently allow the Justice to pretend that their opinion is completely neutral/technical with no personal choice involved, even in cases where the justification is tendentious to an absurd extreme, and to attack those who disagree as radical unprincipled activists with no respect for the rule of law. They absolve the Justice from taking responsibility for the consequences of the decision.
Both originalism and textualism are easily shed by their adherents when insufficient originalist/textualist justification can be found for the desired decision, and following the obvious original intent and plain textual meaning of the statute would lead to an outcome the Justice dislikes.
Textualism involves interpreting words with the same meaning that they would have had at the time whey were written.
Originalism involves interpreting words in the same way they would have been intended at the time when they were written.
To express the crux of the difference, I've seen multiple sources use the example of "cruel and unusual punishment".
Textualism would look at the words: what did "cruel" and "unusual" mean in the 1790? Do those definitions describe a particular punishment?
Originalism would instead consider intent: would a particular punishment have been considered to be "cruel and unusual" in 1790?
Beyond the obvious, what they have in common is what they don't consider: purpose, history, or present meaning.
For fun:
Purposivism would consider the purpose of the clause: is a punishment the sort of thing the clause was written to protect against?
Doctrinalism would look at the way the clause has been interpreted by the court in the past: how does the punishment under consideration compare to punishments previously considered cruel and unusual?
Structuralism would examine the clause and its relationship to the rest of the document in which it was written: perhaps the fact that the clause follows "Excessive bail shall not be required, nor excessive fines imposed ..." offers guidance.
Judicial pragmatism would consider the context, apply inductive reasoning, and consider the future implications of a ruling. (I don't think I've summarized this one well https://www.iep.utm.edu/leglprag/#H2 may be useful.)
This often leads to the same result, but can sometimes produce divergent results. The drafters of the equal protection clause of the 14th amendment, for example, probably didn't intend to create a framework for striking down laws that treat women differently than men. Ginsberg's brilliance as an attorney was to make essentially textualist arguments that convinced courts that--regardless of what the drafters meant to say, the words they actually used plainly apply to discrimination between the genders is it did to discrimination between races.