I am unable to articulate the difference between these tags. Looking at the questions did not help. Should they be merged or setup as synonyms? If so, which one should we keep?
World building is probably somewhat larger in scope, in theory: you could develop a campaign within an existing world. In practice I don't think there's a ton of difference. I would say campaign-development is the right parent tag; it focuses on the activity of roleplaying rather than being a term that's used as often in writing fiction. Me am purist. Grunt.
Edit: as per mxy's comment, I don't think there's a need for quick action here -- there could be a difference, and if one develops or is encouraged that'd be nice.
For me, campaign development often suggests a smaller-scoped activity of adapting an existing setting for a specific group of players.
World building, on the other hand, suggests creating a setting that can be used for many "campaigns."
Specifically talking about D&D games, campaign development often entails using the default setting or a boxed setting (Points of Light, Forgotten Realms, Planescape, etc.). World building always means creating a new setting.
I think they're very different activities and would like to see the tags kept separate.