From a writing and production side, the Madame Gao character became very complicated. The original plan for these Netflix series was a Daredevil season, Jessica Jones season, Luke Cage season, Iron Fist season, and a Defenders series. This changed with the success of Daredevil's first season being so popular and well received, and so Netflix wanted more of that as soon as possible while not wanting to change budget plans. Gao was in the first season was subtly setting up Iron Fist (the symbol stamped on the drugs is the symbol of the Steel Serpent), however during the time they were filming season 2 there was a lot of doubt if Iron Fist would get his show at all, so her appearance in season 2 had to be kept simple, which is disappointing, especially now that we know the Iron Fist show will still happen.
As far as the bigger world, I agree that I want it, but I understand the reasoning behind avoiding it so far. Historically most Marvel villains that appear in the movies and show don't get to come back for further mischief, with obvious exceptions of course, so "going through" villains that may be better saved for Defenders stories or other characters does make sense. They stuck to things they had already set up the first season, The Hand and Stick, while introducing Elektra and Punisher so there were some fan favorite new characters. They played it safe, however I think there is still plenty of time to establish the larger world.