Are jets deliberately excluded from the "Complex airplane" definition? A jet aircraft seems for sure very complex as such. But, referring Wikipedia, a "complex aircraft" (as legally defined) has:


A retractable landing gear
Flaps
and A controllable pitch propeller


And there is no propeller in a jet.

What are the reasons of defining "complex aircraft" so that it does not cover jets? Are these reasons other than historical?
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.