I understand that, what I’m trying to understand is if there’s a claim being made that such machinery is especially desirable in this circumstance... is this claimed to be “the way you have to do it in pure languages” or “a really nice way of doing it, which is enabled by language purity”?
Effects are different because side effects are impure which is not allowed by default in a pure language. Machinery is needed to hide the effects in effect-managing containers so they don't contaminate pure code.