Projects do not exist in isolation. The vast majority of projects affect people and processes already active in an organization; those impacted by the project cannot stop doing what they are doing until the project is completed. They will have other things to do, and their interaction with the project teams is, at best, a distraction or, at worst, a nuisance.
It is essential to make the best use of everybody’s time. Project-related communications may distract stakeholders from their job and, therefore, are not at the top of their priority. The project team sees them as a necessary evil but managing contacts with other stakeholders takes a lot of time.