DNF wasn't just another DN game. I enjoyed it for the Nostalgia, but it was far from a good game in any respect. It didn't have anything that made Duke Nukem good, but what most people forget is the reasons DN took so long, and the reason Gearbox took over and released the shit that was DNF.
Most of the 10+ years it was being developed was all legal battles and no actual game development, when Gearbox got it, it was a pile of shit, and they did their best at polishing it to make a return.
The main reason Gearbox bought Duke Nukem was because Randy loved Duke and didn't want to see him die. I think that Gearbox pushed DNF out so they could work on a new Duke game from the start. There is no official word on this, but it is just what I think. If anybody expected DNF to be even mediocre, they had no idea behind its creation and the legal battles.