So I may follow @JohnSmith because he’s a known dev in the JS community and tweets about JS, but he also tweets about his country’s politics, what he ate at lunch, and engage in heated debats about pineapple on pizza I don’t care about.
You're following the person, not the vision you have of the person. If you're interested in just posts about a topic then Twitter isn't the platform for you.
If someone says "I wish X had feature Y", answering "then X isn't for you" does not contribute to the discussion. Products can change and feature requests shouldn't be dismissed on the grounds that the feature doesn't exist yet.
In this case it certainly could, and is almost already implemented (in the form of both the "hashtags" and "topics").
You're following the person, not the vision you have of the person. If you're interested in just posts about a topic then Twitter isn't the platform for you.