This was purely a business move.
With the death of Russell, there was a power struggle over who would take over the corporation and the religious sect. 3 separate religious organizations emerged, but it was Rutherford who took over the corporation.
Rutherford wanted it to be blatantly clear which sect was over the corporation. Rutherford adopted numerous doctrines and the name "Jehovah's Witnesses" to be sure the public knew the were separate from everyone else. All the prohibitions on holidays, military service, abstaining from blood, etc. are results of this policy of separation.