Apple laptops are known to come with hardware with very shitty open source driver support, there's not alot Canonical can do if they don't get good drivers for the various hardware components.
2) They could improve the other aspects of the experience that is crap on Apple hardware, like display connection/disconnection, sleep/wake, battery life adjustments, keyboard layouts, et c. It takes about a full day to make a mac not suck after installing Ubuntu.
E.g. the 2016 Apple MacBook Pro with TouchBar supports DisplayPort-daisy-chaining, while under macOS you can only daisy-chain monitors if they support Thunderbolt.