Apparently Joe, having not been President before, didn't like anyone Trump liked, and dismissed them.
But now, growing into the office of President he seems to have realised that being 'king' of the free world that is a bad idea.
The President has to, as far as possible, be all things to all people.
US is the largest investor in Australia.
CIA has a base at Pine Gap, Australia.
US drones are guided from the clear skies of outback Australia, reportedly.
US has an annual trade surplus of $28bn with Australia.
Australia has giant telescopes that assist tracking US satellites and space ships to Mars.
etc.
So he can't really just dismiss it and say no to everything.
Big business etc would likely not be pleased.