The issue with the Hobbit flicks was entirely Jackson. he changed the look of designs, where characters showed up and the script very close to release dates, for apparently no reason other then being fickle. There was never a reason to change out Azog for Bolg a month before the first films release, and completely redesign him. Or to add Bolg back in a month before the release of the second film, and then completely redesign him. Remember at least Bolg was originally practical and he filmed the entire trilogy that way.
Also it is unfair to say there was no preproduction. First of all, GDT worked with Jackson in the first place for 2 years. Then after GDT left, Jackson spent six months apparently doing nothing until October were he appointed himself director and then had 5 months more of preproduction.