Because they'd need to be an accredited journalist, and the presenting of any kind of proof to that end would be enough for three-letter agencies to wiggle their way into a compromise of the system - including the fact that glenn may send his old buddy frank in to collect his phone, so better give either one of them one of the tainted ones.
I misread the original proposal a bit and had assumed it'd be a mail-in-service, but with even determination the three-letter folks could probably leave spiked devices in the stores glenn would be likely to walk into. This is more reasonable but I still have reservations.
Keep in mind Glenn knows this too, so presumably would be somewhat wary of his "local" Apple Stores, and could instead choose to randomly drop into stores when travelling to unexpected and unannounced places.
It's not like _any_ journalist would trust this service at an Apple Store in Saudi Arabia, and probably not the UAE, Oman, or Qatar either. (Or may other countries.)
Being "not a perfect and universal solution" doesn't make it worthless. Snowden isn't about to stroll into Apple Store Moscow to take advantage of a refurbed iPhone. I suspect things would be different if Omar Abdulaziz could have dropped into Apple Store Toronto and swapped his Pegasus-infected phone over...
If it was set up well the journalist could have the exact new phone in hand disconnected from any wires that might flash it before announcing he was a journalist. I don't think there is a way with current technology to discretely have people or computers setup to recognize Greenwald (let alone all his friends) in a good percentage of Apple stores before the transaction is completed. Even if it is possible to identify Greenwald and friends before the transaction that access is probably only available to the actual NSA, not ex NSA employees.
On the other hand - you've now identified the phones for remote exploit. Also identifying which journalists are significant enough to be beneficiaries of this program is probably hard.
I misread the original proposal a bit and had assumed it'd be a mail-in-service, but with even determination the three-letter folks could probably leave spiked devices in the stores glenn would be likely to walk into. This is more reasonable but I still have reservations.