It's mostly due to higher "soft costs" such as complicated/slow permitting and high customer acquisition costs. Australia has a higher minimum wage but much lower costs to get a rooftop system installed.

"How to cut U.S. residential solar costs in half"

https://pv-magazine-usa.com/2025/07/11/how-to-cut-u-s-reside...

Birch points to Australia, where he said the average 7 kW solar array with a 7 kW battery costs $14,000. That equates to $2.02 per W, with batteries included.

“You can sell it on Tuesday and install it on Wednesday, there’s no red tape, no permitting delays,” said Birch.

...

In the United States, that same solar and battery installation averages $36,000, said Birch. Permitting alone can take two to six months, and the cost per watt of a solar plus storage installation is up to 2.5 times the Australian price, landing at $5.18 per W.