According to the WT......the reason they abstain from blood was because it was a law given to the nations, not just the jews. It was a law given to Noah after the flood. Since Noah is father of all nations, it was binding on all generations. That's why it was decided upon by the 1st Century christians to keep that law in force while accepting other practices of Gentiles, like it was ok to not be circumsized. They said the Law was nailed to the torture stake, so all Jewish laws were to be replaced by the law of love, and Acts 28: to abstain from blood, fornication and idolatry.
So thats whats so upsetting that they go back to the Mosaic law and say no tattoos, need 2 witnesses. They pick and choose.