It's one less thing to worry about when I just want to get on the plane. My paper ticket isn't going to lock before I get to the gate, or not be bright enough. I won't have to "play" with my ticket to keep it active and proper for the scanner.
I think I held up an entire flight for nearly an hour because the QR code on my Graphene OS Android phone scanned fine at the TSA checkpoint but didn't scan at all at the gate. They ended up letting me on the flight without properly registering that I boarded in their system. That triggered some crazy security hold that prevented the crew from obtaining permission to pull back from the gate.
That's not a thing. They're literally just cameras looking for a QR code.
And unlocking your phone and adjusting brightness is pretty effortless, I dunno. I already do those things lots of times a day.
Then you print a boarding pass at the kiosk? But I've cracked a phone once in ten years, it's not really something I'm worried about.
And paper isn't reliable. For most people, you're much more likely to lose a random sheet of paper than for your phone to suddenly permanently stop working.
Those kiosks are gone from many airports. You're going to have to wait in line to get anything printed. And if you fly Ryanair it will cost you over 50 euro.
Some airlines in Europe check both the boarding pass and the passport/identity card at the boarding gate, to ensure people haven't swapped boarding passes within the airport. I think I see this on flights outside the EU, but I'm not sure.
It takes time to look up a passenger on a computer.
The plane will be delayed if they have to do that for everyone while boarding.
I'm just speculating but if they can simply do a name+DOB-based lookup at a counter, it seems to me like the boarding pass thing might just be for historic reasons where people would feel weird if they are suddenly tracked based on personal details instead of a ticket
And yet for me one time earlier this year said QR code on my Graphene OS phone scanned fine at the TSA checkpoint but refused to scan at the gate, leading to mayhem as the crew couldn't figure out for nearly an hour why the number of people sitting on the plane wasn't equal to the number of people who they registered as boarding.