The problem with oral exam is that it’s done serially student by student, which can be infeasible with large classes. The grading is also highly subjective.

Written exams are also not best suited to project-based classes.

What’s the best way to grade students in classes with coding projects?

Its serial nature also means that an evaluator's standards can drift from students with early exams to those with later exams. Oral exams can introduce issues of sex and ethnic biasing.