#5 – Hide or Remove Starkiller Base
In A New Hope, the Empire has just finished construction of the Death Star, an enormously expensive project that took years to build. They did a good job keeping it secret, but Alliance spies still found out about it and stole a complete technical readout of the station before the galaxy at large became aware of it.
In The Force Awakens, a resurgent but still much smaller First Order builds a bigger, more powerful Death Star through the core of an entire planet. Somehow it goes either undetected or ignored by both the New Republic and the Resistance until after it’s been used to destroy several Republic worlds (the import of which is yet to be seen).
Something’s gotta give.