There's a lot of people who aren't very tech savvy who get checked in by a family member who sends them a text with a screen shot of the barcode which they can scan at the kiosks if they need to print out a bag tag & scan at the auto bag drop.
Many people wouldn't have a clue what NFC is or where to find it on their smartphones assuming it's even activated.
Some people don't even have a frequent membership or do but have no idea what their ff number is. Even if they are a member & have the app they won't always be signed in never mind remembering their password.
Being able to access your electronic ff barcode is a great workaround when your QR code boarding pass drops out because there's a delay & the flight has been retimed assuming you haven't saved the boarding pass to your Google or Apple Wallet.
Perhaps I'm not making myself clear here. I'm suggest BOTH codes and NFC are available to be used. Im suggesting ADDING new tech without eliminated old tech. I'd also contend that the majority of the population know how to use NFC even if not by name. Ie, the use it to tap and pay for things using their phones and watches.