I think he just felt the students wouldn't be able to handle the linear algebra aspects of QM. Strange notion, given that all the students were seniors, and had all taken a linear algebra course from the math department.

Probably wanted less formalism overall.

Like when I took an E&M course in the EE department, and the professor insisted on teaching only the integral forms and not the differential forms of the Maxwell's equations (i.e. no divergence, curl, etc in the whole course).