There's a reason we don't use PN/RPN every day; most tend to think in terms of direct relationships between concepts, not a concept stack that relationships operate on. Parenthesis help us read LTR while allowing nested evaluation.

Experiment:
You and I should go to the beach.
beach you I ~and~ ~go~ ~should~

Dogs and cats are like brothers and sisters.
Dogs cats ~and~ brothers sisters ~and~ ~like~

Mathematics is similar. Even many PN programming languages, such as Clojure, provide alternatives for LTR evaluation.
(+ 2 (- 4 5)) can be written as (-> 4 (- 5) (+ 2))

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