Speaking as someone who's worked on both creative and technical writing teams: It's a mark of poor management. The lead writer's job is to make sure that everyone involved sticks to the project theme and a consistent voice. And then it's the editor's job to double check that consistency.

It's no different than animation: lots of different animators, but you don't see SpongeBob changing art styles every frame because a different artist drew it. The visual producer makes sure everyone sticks to model and style.

WoTC adventures are written more like anthologies than singular adventures, which is an issue if it's supposed to be a unified project.