That's a huge difference.
When it's mandatory, school must find a co-op for you if you cannot find one yourself.
That leads to high % of students in co-op (i.e., work experience), better placements, overall better job (on average).
When it's optional, the co-op participation rate is low.
Obviously, T10, T20, T30 students really don't need a co-op.
But a school at NEU level (or U. Waterloo in earlier days) really pushes B-level students higher.
To the point now NEU starts to attract A-level students.