Because, followers do not lead to that person reading you, unless they follow very few. It's mathematically impossible for anyone but David Perlmutter to read anything close to the number of writers people tend to follow. Following just puts us in the hands of the algo. When I want to try to see everything a writer posts, and I am judicious with my bandwidth in this regard, I subscribe. Yet even that does not always work as mysteriously, or not !! the email notifications often "glitch" my ass.