Independent authors put persistent effort into collecting email addresses while treating social media as secondary. The preference reflects a difference in who controls the connection to the reader.
A platform audience is rented
Followers on a social platform are reachable only on that platform's terms. What proportion of them see any given post is decided by the company, not the author.
Those terms change without notice, and accounts can be restricted or lost with no recourse and no way to contact the audience afterwards.
An author who has spent years building a following on one service can find its reach substantially reduced by a product decision made for unrelated reasons.
An email list is portable property
Addresses collected by an author can be exported and moved between providers. The relationship survives any single company's decisions.
Delivery is also direct rather than mediated, so a message reaches the inbox of everyone who subscribed rather than a filtered fraction chosen by a ranking system.
This matters most on release day, when the value of an announcement depends entirely on how many of the right people receive it within a short window.
Email providers can still filter messages, but they do so on rules an author can work with rather than on a ranking system that is redesigned every year.
The list concentrates the readers who buy
Someone who supplies an email address to hear about an author's next book has already demonstrated intent. A casual follower has demonstrated nothing.
A modest list of committed readers therefore converts to sales at rates that a much larger social following will not approach.
Concentrated launch-day orders then improve retail ranking, which brings the book to readers who were never on the list at all.
Lists are built through the books themselves
The standard method is an offer inside the back of each book, exchanging a free story or a first-in-series title for a subscription.
Every book already sold therefore keeps recruiting, and the list grows in proportion to the catalogue rather than to time spent posting.
Readers who arrive by that route have finished a book before subscribing, which makes them markedly more valuable than names collected through a giveaway.
The obligation attached to it
A list has to be written to regularly enough that subscribers remember signing up, or open rates collapse and the asset quietly stops working.
Authors who treat it as a channel for announcements only tend to find it decays, which is why most successful lists carry something readable between releases.