we personally have found that it often is rooted in lacking planning for the setting. Considering how much has to be done for a sheet in one, how many aspects are involved, a GM either needs careful control over what each puts in, or strict rules to ensure a modicum of balance. The latter of those requires a lot of planning before launch, the former a lot of work after it is released.

Having an overarching plan tends to improve an NRP. Without a "mission" to the NRP, it'll often stagnate due to not enough players being good at initiating engaging plots.

that's how we see it, at least.