Because it's actively user-hostile. It's not that we can't figure it out, it's that it takes extra effort and creates a problem that shouldn't be there in the first place. If things like ThreadReaderApp or Nitter can present the content in a more accessible & pleasant form, Twitter should be able to do so as well.
I see this and would argue it’s not user hostile. Rather twitter’s target users are those who sign up and log in to view and consume content so they can target. It’s not a hostility towards user but rather a non-catering to its non-users. For the majority of content , tweets and threads are not an issue. They easily consume it and if they don’t want to deal with the format they utilize tools that utilize Twitter’s API.