Many people have a wrong perception of TDD. The main idea is to break a large, complicated thing into many small ones until there is nothing left, like you said.

You're not supposed to write every single test upfront, you write a tiny test first. Then you add more and refactor your code, repeat until there is nothing left of that large complicated thing you were working on.

There are also people who test stupid things and 3rd party code in their tests and either they get a fatigue from it and/or think their tests are well written.