Yeah...came here to inquire about that. It's odd: auto downloaded issues (those you follow) delete after 30 days or sooner if your storage is tight, but manual ones can't be deleted. And it being an Apple app, not sure you can delete the app and start over, which would be a workaround.
Texture was great: you could manually download a bunch for the plane flight, then manually delete them afterwards.
Means I can only use it on macOS.
Seems pretty lame; what's the rationale for this????
EDIT: apparently one can delete the entire News app and it's data from an iOS device. Not as nice as being able to manage what to keep and what to delete on one's own, but something.