Thanks for your question, Michael.
Like many traditions in the Australian Parliament, this practice is inherited from the United Kingdom Parliament where the Monarch does not enter the House of Commons or ‘people’s house’.
The convention has existed since 1642 when King Charles I, accompanied by armed guards, entered the House of Commons and attempted to arrest some of its members. He was unsuccessful in making any arrests and thereafter no king or queen has entered the House of Commons chamber.
The tradition continues in the Australian Parliament where the Governor-General, as the official representative of the Monarch, does not enter the House of Representatives chamber. This means that when the Governor-General opens a new Parliament, he or she does so from the Senate chamber.