What do you think of this article about McD's importing beef from Australia because American beef doesn't meet their standards for leaness?

This is the article.
Australian beef is grass fed, not grain fed, which makes for a leaner beef, and they are not fed the mass amounts of antibiotics that American beef is fed—(The article gave me the impression that feeding the cattle grain makes the antibiotics necessary…?)
This is so curious to me. Why wouldn’t American ranchers opt to grass feed their cattle? It’s so much cheaper than feeding them grains.
Apparently Australia’s government standard for beef is also higher than America’s government standard, which is another reason McD’s buys from them.
Thoughts?