Why is it best to have six or less life-cycle phases in an epm system?

In Enterprise Project Management (EPM), the projects may be tackled with a technique known as the phase-gate technique. During this, projects are divided into phases and each phase has its own gate, which are basically points where essential decisions need to be taken. If there are too many gates, the team undertaking the project will be too caught up with reviewing the gates rather than managing the project itself. This inevitably leads to a lot of wasted time.