Fangraphs says it's the lack of competitive balance that is causing the slow off season, that top teams don't need to improve and second tier teams are too far behind to justify spending big money. They are of course wrong. Without the CBT, there would be enough teams trying to make 10-15 game improvements to sign the middle tier players and the Yankees and Dodgers definitely would not be cutting payroll.

https://www.fangraphs.com/blogs/maybe-super-teams-are-ruining-the-off-season/