you can still buy them, just not in Apple Stores.
Apple is not going to sell or stand behind a product that puts an extra layer between the finger and the screen. Apple did not intend for their devices to have protective screens, nor did they intend for them to be used with protective screens.
Apple device screens are among the most durable and scratch-resistant you'll ever find. There's no actual need for any screen protection.
As for the ban, screen protection kind of defeats the purpose of oleophobic coatings, and does send the message that Apple's screens are in need of protection.
I've stopped using plastic screen protectors for my iPhone long ago, preferring a nice, thin, plastic/transparent backing. Works great.
Further, you can get your screen protectors elsewhere, just not in Apple Stores. No big deal.