Comment by atombender

I think part of the problem is that the people working on Postgres for the most part aren't PhDs, and Postgres isn't very state of the art.

Postgres implements the ancient Volcano model from the 1980s, but there's been a ton of query optimization research since then, especially from the database groups at TUM Munich, University of Washington, and Carnegie Mellon. Systems like HyPer and Umbra (both at TUM) are state of the art query planners that would eat Postgres' lunch. Lots of work on making planners smarter about rearranging joins to be more optimal, improving cache locality and buffer management, and so on.

Unfortunately, changing an old Volcano planner and applying newer techniques would probably be a huge endeavor.