In my experience, most people on twitter won't click to read long form content if it opens in a separate view. They won't read past few tweets either. I believe most twitter users don't want to read beyond 280 characters. A thread provides them an opportunity to comment on any 280 characters section they have actually read.

They should have provided similar interface to typefully to write long form tweet and a button to view all tweets as an article like threader app while keeping the same UX/UI with little changes.