The question in question :
Why do we not name different piano keys with different letters from A-Z? Why do we only use letters from A-G? Wouldn't keys with different letters be easier to memorize and less likely to confuse for the other?
If asked from the perspective of someone who knows very little about music - who perhaps doesn't know anything about scales and how they (usually) repeat each octave, and instead might assume that the key names are purely for disambiguation (and not realise that they are also chosen to show relationships between notes), this question clearly makes sense.
It was closed as a duplicate of Why Seven Principal Tones? (Which itself is not a great question - 'principal tones' aren't really a common term, and the top answer is "We don't know.")
The question that was closed as a duplicate of, and another comment by a mod, suggested some more answers as to why we have 7 notes in the scale. That information is clearly relevant and would form part of an answer, but can't in itself be a complete answer to the OP's question, because we don't know if the OP understands what a scale is, or how (or why) scales repeat over the octave - all of which he'd have to understand as well as the information presented in the suggested duplicates to clear up the question they actually asked.
So - should questions be closed as duplicates of more specific questions at a higher level?