One possible reason I can think of is that phone camera apps will not proactively read PDF417 barcodes like they will QR codes, thus discouraging people from thinking they can scan and decode them.
My phone's default camera app can recognize QR and UPC (and certainly other things; but I have other tools that I usually use when actually-using barcodes so I'm not that familiar with this part of the camera app), but it doesn't seem willing to do anything with PDF417.
My phone's default camera app can recognize QR and UPC (and certainly other things; but I have other tools that I usually use when actually-using barcodes so I'm not that familiar with this part of the camera app), but it doesn't seem willing to do anything with PDF417.