Policy in id software in Carmak days was to GPL the last engine as soon as a new one was released. The business model was to expose more people to the old engin

Policy in id software in Carmak days was to GPL the last engine as soon as a new one was released. The business model was to expose more people to the old engine, weaken competition and offer consultancy and customization (I think). They basically showed that it was possible and profitable. It is a shame this ended after doom 3.