Why does an opthamologist and not an optometrist oversee eye examinations for optometry students?

Not sure: Several optometry schools have ophthalmologists as associate professors, especially for clinical rotations. The idea is to let students see as many eye conditions as possible during their training, and ophthalmologists tend to see a wide variety of diseases. To be sure, optometrists also oversee the students, but the variety breeds a more well-rounded doctor.