That is because they are badly designed. A system that is better designed will not have these problems. Myself and other people have mentioned some ways to make it better; I think that redesigning the entire computer would fix this and many other problems.

One thing that could be done is to specify the interface and intention instead of the implementation, and then any implementation would be connected to it; e.g. if it requests video input then it does not necessarily need to be a camera, and may be a video file, still picture, a filter that will modify the data received by the camera, video output from another program, etc.