Apparently, and this may be Apocryphal, but Rutherford struggled long and hard to come up with a new name, to differentiate them from the Bible Students who were still going strong, but were loyal to the teachings of Russell, and not Rutherford's.
He said it came to him " during the night". Quite how much liquor he had consumed before retiring who knows ? but if he had thought about it, to take a Scripture from Isaiah and apply it to a supposedly Christian group , and give it a name from pre Christian times, was a big mistake which would make the JW's sound weird to all and sundry.
Maybe he did think about that, but went ahead anyway, not bothering that the new Testament clearly says we should be Witnesses of Jesus.