This is why some organisations do have this approach though. One of my current clients has a system where you register your basic details, then do an SJT, and then complete the application form if you are successful.
Although in many ways it is fairer to the candidates and they "waste" less time, it does make the process more drawn out. Also the more individual stages you put in, the more people will not complete the recruitment process. Recruiters will regularly lose somewhere between 20-40% of candidates through non-completion rates at each stage.