I thought the 'if the level of interactivity basically amounts to a form' of top-level comment sums it up nicely. Many are SPAs for the sake of it, similarly to packaging a website as an 'app' but not doing anything native, offline, or that really warrants it being its own app at all other than getting homescreen space on iOS.

(Totally off-topic: I can't believe Apple still doesn't let you organise that however you want. It's sort of a small thing, but also so in your face, by far the most immediate turn-off to me of iOS.)