I think it's just a vertical integration thing. They know what's in the machine and they can make sure that their suspend path puts every peripheral to sleep. Linux has no idea what's in your machine and there may be some device in there somewhere that freaks out if the machine goes to sleep without saying goodnight. Even a 50mW draw will destroy the suspend power budget. Chromebooks have similar vertical integration with respect to ChromeOS and they also enjoy long sleep life. Hypothetically an integrator like Framework can also guarantee this but I can't vouch for it being true, and they would not have any control over Ubuntu updates after the laptop is delivered to the customer.

Just to beat my favorite dead horse, this is why the insistence on SO-DIMMs "BEcAuse it's rEpAIrAble" has wrecked the reputation of a lot of laptops. DDR on a stick is fundamentally hostile to sleep power draw. Soldered-down LPDDR memory has always been massively superior for energy savings, and LP-CAMM finally solves the issue.