having a degree makes a lot of sense, especially for cadets coming out of flight school.
differantiation between cadets is incredibly small and normally only based on the amount of groundschool fails, scores and first/second series IR/CPL. Also based on the flight school report obviously. But this is only based on your skills during training.
A degree will broaden your vision, improve your learning abilities and you will do lots of group projects which will help your decision making, leadership and teamwork abilities.
Off course you won't use a lot of the things you have learned during your degree in the cockpit... however, it is an assurance for an airline that you are able to do more in life than just fly a plane.
This still means that not having a degree is fine too, but that airlines will give preference to candidates that do have a degree makes sense to me. It simply reduces the training risk for an airline.