The whole point of AP and AP redemptions is to only offer the seats that have the least probability of being saleable for revenue in the entire system. That's how they can maintain the 'fiction' of AP rewards being worthless, and hence, not a taxable benefit, a bribe, etc. to the people who accept them. And of course, only consider the liability to be minimal on their balance sheet when the auditors come a'knockin.

Considering that the domestic int'l widebody seats are so coveted to the extent that AC actually feels justified charging a 'surcharge' for them over the narrowbody product, it doesn't make a lot of sense that they are many that are available for redemptions. And being as coveted as they are, of course they disappear rapidly.

Of course, nothing stops someone from redeeming a J reward, for a later flight, showing up early, and going standby. The standby list clears before the upgrade list.