Because if you move from one project to another you want to see a familiar implementation of Request class or ORM from a framework rather than reverse engineer

Because if you move from one project to another you want to see a familiar implementation of Request class or ORM from a framework rather than reverse engineer custom-built undocumented untested replacement for this. It may make sense if custom framework is a magintude order better, but if it is the same as a standard framework or worse then it is not worth to spend time on it.