I don't think believing why the most valuable company in the world with the highest and thickest walls around its garden, and a track record of not playing nice with others, is doing this, requires much explanation except that they want to kill the possibility of anyone bypassing the toll gate to the said garden.
Apple has no way of enforcing any kind of platform fee for PWAs since the developer does not need to interact with Apple at all. This financial conflict of interest is why the availablity of the full PWA feature set is desirable to developers and undesirable to Apple.
