It's the entire overall premium and CC/points market in the US. A few of these programs I'm a little too intimately familiar with from spending a little too much time on them. In general, every airline knows that the award AND premium demand from the US is particularly high. I think every airline market analysis will confirm that fact. Not sure how much of is deliberate (e.g. they know the demand is so high that they deliberately reduce award availability), and how much of it is genuinely organic award demand (demand is so high that everyone with award alert tools instantly books any availability). You'd need internal revenue data to know that for sure of course.

For CX, for example, they do not appear to EVER release F awards at any time on any US O/D routes beyond the initial few seats during schedule open, which is available only for CX elites well before AA can book. This is despite literally having plenty of lowest-class F available right before the flight. Similar story with J and Y, even with many seats last minute they would rather gamble on upgrade bids or last minute bookings than releasing award seats. And when they do occasionally get released due to *deeply* empty cabins, I've only seen maybe a few openings for high tier partners like JL IIRC and not AA), and I think a single time ever for AA. So AA is a very, very low availability tier partner for CX, at least on US routes. It's always possible that this is from people with bots so fast that you never see the opening, but I've never seen any internal data

Totally different story for LHR-HKG flights. I routinely see F awards last minute get released (in fact, a lot of the F availability that's shown on CX AsiaMiles is actually a connecting US-BA/AA-LHR-CX-HKG flight), and quite a few open awards probably fly without ever being redeemed. One of my observations was that it's quite rare to ever see a flight take off with any remaining award inventory on some of the popular US routes (when I see USA-TYO, or USA-HKG, it's pretty much always gone by the next time moment I check)

For QR, similar deal. Most premium US inventory (90%+?) is only available directly only QR's program and some select partners. And even then, US-DOH inventory always instantly gets taken, but any other long haul across the world will often remain for some time. I've never seen any inventory also show up on AA, but other OW partners often can't see it either.

For JL, I do think AA more or less has the best inventory, other than on JL's own program. People sometimes get confused because of their dynamic awards, but it's pretty rare to see genuine lowest-award J inventory for US routes even on their own program. One step up from the absolute lowest mileage redemption class gives you a lot more opportunities. You see the same thing when booking AA metal with AA miles, vs using JL/AS/etc. My understanding is AA/JL have a pretty close business relationship because of their codeshare/(joint business?) arrangement on US-Japan routes. The JL program was literally offering double miles for flying on JL-codeshare AA metal recently. It's just extreme premium demand. FWIW, I rarely see any AA flights on CX, even when it's available to QR/EY/AS/QF, so I believe the lack of inventory is mutual there.

Anyway, maybe this is new thing for OW, but I've been seeing it on *A for quite a while. Some *A partners see more ANA inventory, some see less, etc. I've had customer support agents from different airlines explicitly tell you that it's their partners that simply don't release inventory to them.