Most people have anxiety about change. Know that when changes are being initiated, resistance will surface. The new change goals and benefits are not accepted by the people who have to function with the change. Neither the reasons for change nor the benefits of the change are adequately or effectively communicated. People fear the unknown and can't predict the outcome.
People fear failure.
People like the current situation. The purpose for change is not clear or relevant. People dislike the person recommending, announcing or implementing the change. People see change as an attack on their performance and react defensively. The timing of announcing the change was wrong or perceived as wrong by the people involved in it.