Please think that Threads/X is just an app that lets people post shit on their timeline and engagement. While they both may appear to have similar format (brief posts, trending, timeline etc etc) their algorithms and use cases are completely different. When Twitter started, it was a platform for fast dissemination of news straight from silicon valley. Later on, it became a platform for people to share political and social views, a platform for celebrities to update their fans about their thoughts,maybe shit post and what not.
And then it made eco chamber for different sides of politics, and thats how it got all engagement. Eventually the bias came in, but then X solved it to a greater extent.
Threads thought it could just copy the format and be done with it. They probably thought of linking it to the Instagram account(the biggest mistake) would give them a huge distribution, and threads eventually ended up being another instagram, completely redundant.