It's because defining requirements is someone else's job, so if you get involved, you will be doing part of their job while you might already be working at your capacity.
The Agile style user stories that often lack technical details because the author doesn't know enough about the technical details means the developer is the one actually writing the requirements (usually as they are doing the work).
The Agile style user stories that often lack technical details because the author doesn't know enough about the technical details means the developer is the one actually writing the requirements (usually as they are doing the work).