It isn't odd if you think about it. Russel and Rutherford needed some authority to which they could appeal. The bible was and is a great authority to fall back on. Remember that the JWs were a offshoot of the protestant movement which rejected Catholicism but still held the Bible as the unerring word of God. They even called themselves Bible students at first, likely to show that they were going back to the original source and "restoring" the original intent of the scriptures. It may not make sense to us today, but for people in those times having a clear understanding "what the bible really teaches," was very appealing. The pseudo-intellectualism of analyzing Bible prophecy likely also stroked peoples egos as they felt they had gained a secret knowledge that others didn't possess.