Many publishers venture into direct to consumer, but have no clue how to do that in digital (the systems and mechanisms used in the good old days to generate paper issue subscribers do not work anymore). As they have always considered readers as something entirely different from clients (advertisers), systematic newslettering, performance marketing, CRM, churn prevention, winback programs etc. are new to many publishers - and many learn painfully that just offering a paywall and a free month to test (and then hope for the best) just won't do.
Here's an interesting research by the Center for Media Engagement (University of Texas) on what works and what doesn't (at least in the US) to advertise for subscriptions. Surprise: Converting free email newsletter subscribers alongside multi-channel advertising tops the list.
Study/Report as PDF