When you check in online with JetStar, it offers you 2 options for getting and using your boarding pass:
Receive a link by SMS (and not by email) to the boarding pass to be added to the Google/Apple Wallet app. When boarding, you need to open the app and show the boarding pass in it.
Receive an email with PDF boarding pass. This needs to be printed out, and the paper needs to be presented when boarding.
In option #2, what is the rationale for requiring the PDF pass to be printed out? Why can't the PDF just be shown from the screen?
Related question: in option #1, why can't the link be received by email?