Are jets deliberately excluded from the "Complex airplane" definition?
All jets require a type rating. Therefore you don't need the complex endorsement directly (other than needing it likely for your commercial checkride, which requires a complex aircraft). The historical training progression is: simple prop, complex single engine prop (requiring the complex endorsement), high performance (200 hp+, though this one is sometimes not gotten), light multi-engine props, and then finally moving into heavier turboprops and then jets which require type ratings.

Note, my answer is FAA specific, and other agencies might have different rules/interpretations for this issue.