"Why should the writers of an English translation follow Koine Greek grammar or punctuation rules?"
To be consistant with the JWs so called accurate interpretation of ancient scripts. They follow the rules to a tee, why not add that special feature just to be consistant? All capitals-Koine Greek, all capitals English language. Also, it is a bit strange seeing caps for certain words pertaining to humans (for example-YOU) BUT no caps for pronouns (him, his, he) referencing the Creator of the Universe-Jehovah.
"Then to ?YOU? I will cause my spirit to bubble forth; I will make my words known to ?YOU.24Because I have called out but ?YOU? keep refusing, I have stretched out my hand but there is no one paying attention,25and ?YOU? keep neglecting all my counsel, and my reproof ?YOU? have not accepted,26I also, for my part, shall laugh at ?YOUR? own disaster, I shall mock when what ?YOU? dread comes,27when what ?YOU? dread comes just like a storm, and ?YOUR? own disaster gets here just like a storm wind, when distress and hard times come upon ?YOU."28
NWT Proverbs 1