Consider that the real unstated reason may well be that regulators in your respective home countries have passed laws regulating foreign brokers who serve citizens of your country.
This is the usual reason. I think this applies to Australia.
Many countries have recently done so, including the U.S. in respect of non U.S. brokers soliciting its citizens (the inverse situation).
In other cases (some South American and other countries) the U.S. may be the one restricting money transfers to some countries, or imposing onerous verification liabilities on the broker and its bank, for various reasons related to sanctions, tax reporting, prevalence of money laundering etc.
Usually to avoid getting into detailed policy discussions that the representative really cannot deal with, the broker will just say it is for "business reasons."
Your best bet is to switch to a broker that already has a branch in your country, or is otherwise approved by your home country to operate there (e.g. has a branch in another European country in the case of the E.U.)