There is no known data relating to as why no issues of the Coronation were printed at the time of the ascension of King George VI and the Queen Consort Elizabeth.
Australia and a few other countries did not join the many Commonwealth countries issuing omnibus stamps (all stamps from the contributing countries adopted the same design.
Australia issued the first of its coronation series on April 1, 1938 with the introduction of the 5/- and 10/- Robes, and on November 1, 1938 the £1 dual effigy of the monarchs were issued; these were printed by John Ash.
Ten years later on January 27, 1948, a year after John Ash retired, the new government printer W.C.G. McCracken issued a a reprint of the 5/- Coronation stamp, and on November 17, 1948 the 10/- issue was reprinted; and in November 1949 the £1 value was reprinted; again there is no explanation as to why.