I think it might be a buyers demand sort of thing.
2 litre motor with 12kW battery became 2.4 litre with 13.8kW and now 20kW battery.
Fuel tank was 45 litres and became 57 litres.
Corolla's started the size of a Suzuki Swift and are now almost Camry's.
Evolution.
I know the later 2022 Outlander PHEV is Nissen based but if the chassis is mostly retained from the 2020 model, there's a good chance the newer 57 litre tank fits in the same place. It depends on how shaped it is to fit in with what's around it as to how easy/hard it might be to retrofit. I don't have the facility to look at or compare the two models side-by-side on a hoist that a dealer might, or have access to the parts books they have, so I thought it worth asking if anyone else has ever explored this.