William Schnell makes this interesting observation in his book THIRTY YEARS A WATCH TOWER SLAVE, page 71:
"In the Germany of the Weimar Republic everything was going from bad to worse. Democratic processes brought into being by the terms of the Versailles treaty were repugnant to the Germans, because they considered the democratic process and the Weimar Republic as a symbol of their defeat. Unemployment was rampant and hope for better times was fading everywhere. The masses were driven about like lost sheep. Communism on the left claimed millions, the Nazis on the right were growing fast, while the moderate Centrum was shrinking. In the middle, however, were millions who wanted a spiritual and peaceful way of life, and these were the people we were after. We were fishing in the troubled waters of the German population.
"Appearing to them as God's Organization, powerful, unafraid of opposition, we easily became their champions.
"If events had not transpired to put the Hitler movement into control, Germany might have become the first Jehovah's Witness state of God's Organization. The Nazis and the Communists realized this and began really to oppose us as the third force."
If Schnell is correct, then Hitler jailed the JWs because he viewed them as a political threat, not because he didn't like their religious beliefs.