To give a few examples, there is no JavaScript interpreter in Quartz (https://www.adobe.com/devnet/acrobat/javascript.html), nor does it have 3D graphics rendering built in (https://helpx.adobe.com/acrobat/using/displaying-3d-models-p...), or a Flash engine (https://helpx.adobe.com/acrobat/using/flash-player-needed-ac... this has bee removed from the Acrobat install, but used to ship with it)
To support PDFs fully, all of that would have to be implemented on top of Quartz.
To give a few examples, there is no JavaScript interpreter in Quartz (https://www.adobe.com/devnet/acrobat/javascript.html), nor does it have 3D graphics rendering built in (https://helpx.adobe.com/acrobat/using/displaying-3d-models-p...), or a Flash engine (https://helpx.adobe.com/acrobat/using/flash-player-needed-ac... this has bee removed from the Acrobat install, but used to ship with it)
To support PDFs fully, all of that would have to be implemented on top of Quartz.