They made a rifle that was ineffective at full auto, and they wanted a full auto weapon.
So, the M14 was worthless from the beginning. That is (one of the reasons) why the M16 was eventually adopted. It worked well as a select fire weapon.
As for the Garand/M14 comment. The military had explored going with a detachable magazine on the Garand (the only real advantage to the M14 over the Garand) originally, but ended up scrapping the idea.