Why?? Because Witnesses are less into Christ than they are into Moses. When Christ talks about turning the other cheek, Witnesses talk about why the faithful should shun anyone that doesn't see eye to eye with them. The Jewish religious leaders were condemned by Christ for their biases.
Why do Jehovah's Witnesses treat disfellowshipped ones as if they were "dead"? Because the Jews used to do the same! Why do they have a tribunal to hear a judicial case?? Because Jesus told Christians to have 3 elders and make a judgment?? No---it's because this is the way the Jewish courts handled matters.
What is the foundation for a Witness not to take blood? The basis starts in Genesis that blood is sacred and then all sorts of "Hebrew Scripture" texts are used to support that "true Christians" also should refrain from blood.
What Bible books do Witnesses interpret in their publications more than any? The "Hebrew Scriptures also known as the "Old Testament". As a matter of fact, almost everything that is expressed in the OT is said to have a parallel with today's anointed Jehovah's Witnesses and their counterparts, those not expecting to go to heaven!
Nearly everything that Jesus criticized the Jewish religious leaders for, Jehovah's Witnesses do.