Larger caliber rifles resulted in lower capacity mags, making full-auto use impractical. The larger caliber round was designed to kill, and semi-auto encouraged making every shot count.
Another fine theory dreamt up by some goof who assumed civility on the part of our enemies....
I like the description, posted by a New Zealander on a Youtube video, from his veteran RSM who took part in Operation Claret in Malaysia in the early 1960s...he said you could always tell the difference between a “nog” who got shot with an AR-15 and one who got shot with an L1A1...the ones shot with the AR would slump forward and into the boat (that they were using to infiltrate)...the ones shot with the 7.62 NATO round of the L1A1 would fly backwards and OUT of the boat!