The priestly blessings were first recited in the Holy Temple. After the Temple was destroyed the blessings continued to be recited  in the synagogues. When the rebellion was crushed by the Romans and they expelled most of the Jews from the land the Diaspora began. Jews could not own businesses or own land and were dependent on Christian landowners and craftsmen for their livlihood. The rabbis deleted the priestly blessing to enable Jews to get to their work on time. Since these blessing were originally recited in the Temple their deletion was easy to accept.