As a big tribe, many of us have learned the pattern of the treasure maps from Bob's Tales DLC.
Those who don't have the DLC, get more maps and higher quality maps.
Those with the DLC barely get any, and when they do they're primitive or Ramshackle if lucky.
It seems like a typical marketing tactic to entice people to buy the DLC in order to use up those treasure maps that they keep getting. Well played!