Timing is everything. Without the conductor all the musicians are using their own sense of timing. That can lead to disorder as there is no uniformity. Even having practiced together, it's hard to keep everyone together without something singular to focus on. The conductor brings uniformity and is the single "center" to time everyone to.
It's like a fine automobile. A Modern Car is made of many components and these components are made up of hundreds more parts. They are each engineered with precision to accomplish a single task. While all the components, doing all their own tasks just as they were engineered to do, will function as a car when assembled... it still takes a driver to make the car go any place meaningful.
The conductor is the Driver of the Orchestra.