KJVI have a "bad" translation? What translation do you have?
The Greek was translated into the use of the English word 'for' - the most appropriate word to use at the time of the translation.If the Greek word used for "for" in Acts 2:38 means because of why is it not translated this way?
The English word 'for' - from the time it was translated even to this day - like many English words - has many "senses" of the word - each according to context and usage.
At the time of the translation, the people understood how the various "senses" of the word applied to prepositional phrases.
Anyone who understands the English language well enough today should also understand how the various "senses" of the word apply to prepositional phrases.
The translators of your bible version extrapolated the wrong "sense" into a set of words that "fixed" the meaning in a way that does not allow for the true intended meaning - forcing it into the "sense" of 'in order to obtain' rather than 'because of'.
It is the use of the word 'for' in the English language that allows for the proper translated meaning.
Considering the fact that the words 'because of' are actually used many times in scripture, your question is a very good one that some very indepth study of the varied word usage should shed some light on.
Nonetheless, the word 'for' is also used in scripture (for reasons we may not understand unless-and-until we study it at length) - and, when it is encountered in whatever context, it must be examined carefully in the English (and, sometimes in the Greek) to discern the proper "sense" of the word intended.
My use of 'because of' and 'in order to obtain' is based on the modern-day understanding and use of the English language - to illustrate two different "senses" of the word 'for' as it may be used in a prepositional phrase. They are my own personal "closest approximation" phrases for my understanding of two of the different "senses" of the word 'for' - what 'for' means in a particular context-and-use - in scripture.What Bible uses such verbiage?
It is not a Greek question. It is not a translation question. It is a how-we-understand-the-English-language question.