Arnold E, you appear to not get the point. My apologies if you are an experienced commercial pilot and I'm telling you to suck eggs, but every airline has strict rules about the amount of fuel required for every phase of flight. When UA departed the US, they would have had the required amount of fuel on board. Throughout the flight, they may have experienced increased headwinds or Sydney's weather may have changed which could have added a requirement for an additional 60 minutes of holding fuel. If they did not have sufficient fuel to meet the increased requirements to continue to SYD then they were required to proceed to a suitable alternate (observing the required fuel reserves at all times) to take on additional fuel. Noumea and Nadi would also have been available if an earlier diversion was required.
There is absolutely nothing newsworthy about this diversion as this was professional aircrew doing their job the way they should do.