From memory the LCH was originally to have been commanded by a WO2.Army v RAN politics may come into it, remember the Balikpapan Class LCH were originally Army but the RAN ended up taking them of the Army's hands. Crewing a larger vessel may be an issue for the Army, get up into the 45-50m range then you are going from a Crew of 3-5 to 6-10 and probably going from a Corporal to a Sergeant in command.
What was more interesting was the LSMs, operated by the Army that the LCHs replaced, and even more interesting, the LSM MK2, designed to replace the LSM, but cancelled in favour of the LCH. These were all planned as army vessels, able to transport a troop of tanks and other assorted vehicles, plus personnel, stores etc.