It's not that they are incapable. They are unwilling.
Nobody should be surprised that one of the most successful proprietary technology companies on the planet sells highly proprietary technology. The 2011 Macbook Air had a 1.8" PATA ZIF hard drive.
A quick search shows PATA ZIF drives were also used in Thinkpads, Dell / HP / Acer / Asus laptops, and other portables like the iRiver. Replacement drives for that model of Macbook Air are available, doesn't seem like it is proprietary tech at all.
Nobody should be surprised that one of the most successful proprietary technology companies on the planet sells highly proprietary technology. The 2011 Macbook Air had a 1.8" PATA ZIF hard drive.