The key word is 'web'.

Lets say a transit company decides to do away with its train ticketing app and adopt a PWA but as the conductor is checking your ticket you move through an internet black spot that lasts for half an hour, still possible in densely connected countries like Japan and the UK. How can you prove you paid when the app went dark?

The old ticketing app would, regardless of web connection still have that ticket saved and ready to go because you downloaded it to board.