Anecdotally this isn't true. The only time I have heard anything about Stephen King in the past few years has been in relation to a tweet he has made.
I think this is true for many significant accounts on the platform: I'm not going to read their blog or watch their Youtube video, but I'll probably see someone resharing a tweet they have made, whether on Reddit, HN, a news website etc.
Which is where I see the huge value in Twitter: a mainstream platform designed to present content in bite-sizes, appropriate for discussion or resharing. Twitter is a reach multiplier for many accounts for this reason.
People who have not heard of King before Twitter and only hear of him from Twitter are not going to be the people buying his books.
So even if there were significant amount of people like you, he is not gaining anything from people seeing his Twitter. On the other hand, I have relatives who created Twitter accounts only to follow authors they like - the number of curated lists of notable literary figures is a testament to that fact.
I'm not saying Twitter is worthless to writers - readers talking about the books certainly helps sales, but that occurs regardless of whether the author themselves are on Twitter or not, and Twitter is certainly not the main platform people use to discuss books.
