Probably because newspapers are notorious to be the worst of the worst when trying to cancel free deals that automatically turn into expensive memberships.

Common methods are to only allow cancellation through telephone and only have open during work hours when most people can't call. If you manage to get hold of a human being, then you'll have to spend an hour arguing before they accept your cancellation. Then, even if you manage to get through it, you're missing the paper trail so the newspaper can just claim you changed your mind.

As late as yesterday, the Swedish Consumer Agency published a report on the issue.