At the same time white box test cases cannot be written at the initial start of the project. It is so because white box test cases need more architecture clearness which is not accessible at the beginning of the project.
Black box test cases don’t need system comprehension but white box testing requires more structural comprehension.
Structural comprehension is more intelligible in the later stages of project.
For black box testing QA engineer needs to only analyze from the functional perspective which is easily accessible from a simple requirement document.