https://en.wikipedia.org/wiki/Singap...ghts_21_and_22

This flight (and the upcoming QF project Sunrise flights stating in 2026-'27) flies 18-20 hours nonstop which would 'save four hours compared to a one-stop flight'.
I doubt it. I rather thing two hours: extra landing and takeoff costs 2x30 minutes plus one hour stop makes two hours. But, let it 4 hours, this is not the worst issue.
Taking 1-2 extra sets of crew, hunderd(s) tons of extra fuel makes such flights more costly than one stop flights on a similar distance. The extra fuel and extra crew costs paying passenger space, decreasing profits of the flight.
Moreover, LHR-SYD contains more stop airports close to the great circle route (SIN, BKK, DXB), unlike the SQ SIN-JFK polar route.

I think such flights are just prestige of the airlines 'we can do LHR-SYD non stop'. Or is there another reason these airlines operate such flights which cost much more money than a one stop flight.

Your ideas ?