It's much easier to build a gateway API for a legacy system than to extend it. Not disagreeing with you. Honestly, though, software systems for academic institutions are ridiculously complicated, because they are essentially a student portal, a school, a sales organization, a rules engine, etc. etc. all wrapped up into one and interconnected in ways that aren't obvious on the surface.
Do you know that software can be used to build a wrapper layer around other software?