One very important point to note about Abiraterone (Zytiga) is that it's an older ARSI that requires the patient to take the steroid Prednisone with it.

While many patients tolerate steroids fine, others experience a whole range of side effects, even if they can tolerate the Abiraterone itself.

Personally, I've experienced steroid-induced diabetes when on steroids to try to take down the swelling in my spine (I had to go on insulin in the hospital until they finally took me off steroids); others experience heart problems, etc.
https://www.mayoclinic.org/drugs-supplements/prednisone-oral-route/description/drg-20075269
Newer ARSIs like Darolutamide and the other -lutamides don't require a steroid, but they cost many thousands of dollars/month, while Abiraterone is out of patent and generics cost as little as U.S. $30/month.

So it's no surprise that U S. insurers push patients towards Abiraterone as a "still good enough" default treatment, and in some cases might force doctors to work hard to justify a more-expensive drug (or penalise them if they prescribe it too often? I'm not sure how things work down there).