They ended up having to spend A LOT more on the Wrigley Renovation that they thought. The original budget was around $500 million for the park and improvements around Wrigleyville. They ended up spending over 550 million on the park alone, only to have it sit empty for a year. Up until this season the Ricketts have spent as much as anyone not named Yankees or Dodgers.
If you continue to exceed the luxury tax, for a number of consecutive years, the penalties get worse every year. Since the core of the team has obviously regressed to the point that even the most casual fan can see that the roster needs re-tooled, it only makes sense for the team to try to hit the reset button on the luxury tax as well. (The Yankees have done the same thing. Which is why they made us pay Rizzo) Only the Dodgers and Red Sox are over the tax this year.
It's feels crappy right now, but its all in the best long-term interest of the franchise.