MJ has consistently been the highest earning deceased celebrity, and in 2016, was the highest earning artist period (thanks to the ATV Sale) but hasn't been for the last couple of years. The fact of the matter is, just "crappy projects" aren't going to keep revenue flowing and continue when the real money is in streaming content and other things with ongoing support. Music albums, music period, does not accrue much.
Although in reflection, much of their early success no doubt was in the long term genius of holding on to the catalogue...