There's one difference: at HKG the aircraft has access to HAECO for any scheduled mods or installations, etc.

But this aircraft utilization issue is typical of some long haul destinations encountered by many airlines, and most likely that is factored into fare pricing as well.

But why does AA not do an extension?
Instead of flying USA-EZE and sit on the ground for 10 hours, why not do the same thing as e.g. AC and fly USA-SCL-EZE?

Because there's not enough demand for that route. Fares would have to be lower for people to take a stop in SCL instead of taking a non-stop to EZE.

It is a "direct" flight. Not a "stop" flight. You would still sell USA-EZE.

If it stops in SCL on the way to EZE, then it's a "direct" flight but not "non-stop".

And most people will pick the non-stop unless the "direct" is cheaper. So AA would have to lower fares to compete with the non-stop flights.

A while back I checked fares BOS-EZE. AC with its extra stop in SCL was not cheaper than AA, DL or UA. In fact, AA, DL and UA where MUCH cheaper than AC.

Sorry, I just don't see why anybody would pay more to have a longer total trip and an extra stop. [Edit: Especially if you make it one flight number so you don't get extra miles!]

Sure you can find some days where that happens, maybe a lot of people were going YYZ-SCL and there weren't as many seats available.

But look at BOS-EZE right now for Dec 19 with a Jan 2 return (probably the busiest dates you can find), and AC is cheapest at $2,267 (stops in YYZ and SCL) while AA 1-stop is $500 more.

AC has another anomaly going in it's favor which is the connection in YYZ. For anybody from other continents who want to connect to South America, they are able to transit at YYZ, while a connection in the US would mean having to get a US Visa and go through immigration/customs.

Not any longer. Starting March 15, 2016, visitors or transit passengers from other continents must obtain a Canadian eVisa when flying via YYZ or any other Canadian airport.

http://www.cic.gc.ca/english/visit/visas.asp

I must say I was a bit disappointed in the presence of LATAM in S. America. I'm pretty sure they are the biggest airline in S.America based on figures but when I was looking for flights for my recent holiday trip most often other carriers came back with better options.

Partly maybe because the flights I looked for involved touristic rather than business destinations.

AEP - IGR (Iguazu) : Operated by LAN & Aerolinas Argentinas. LAN seems to uses busses to board all it's planes in AEP. Probably cheaper but a bit annoying.
IGR - AEP - SLA (Salta) : 2 times with the bus in AEP. Aerolinas Argentinas had a direct flight between IGR & SLA. Would have been a lot faster.

LPA (La Paz) - EZE : One option would have been with TAM Paraguay but the connection in Paraguay was so bad it would have cost us a day so we decided to go for BoA. Connection in Sucre but a lot faster.

Con for Aerolines Argentinas is their baggage allowance, only 15kg on domestic flights.

If AC had that in its favor, it would fly each route non-stop. But since the market does not have enough demand, EZE and SCL are combined into one route, whereas AA has up to three daily non-stops to Santiago separate from EZE service.

Actually I do know a couple of people that fly AC for exactly that reason although certainly they are in the small minority.

Yeah I was referring to the USA-EZE market as far as OneWorld. Miami 3x (2x AA + 1x LAN) and 4x in summer, JFK 1x, DFW 1x, SkyTeam does have Aerolineas Argentinas 1x to MIA and 1x to JFK, but Delta metal only goes once a day to ATL. Star Alliance has only United daily from IAH.

I've heard the issue at AEP is that while LAN is larger, there's a political issue with them getting actual gates because AR is owned by the government, so they have to do the buses.

AR has the occasional bus at AEP as well.

They've left me stranded enough times that taking the bus from AEP to COR might have been faster