This is a term describing the high proliferation of music schools that train students to become professionals in a field with few opportunities for work, which leads to the proposed solution of higher education for these students so that they can teach the next generation to begin the cycle anew.
The music scene becomes flooded with these graduates to the point the genre itself becomes dominated by professionals. This 'professionalization' causes the music to suffer by prioritizing representation for output that is deemed 'good music' thus reducing representation for the community aspect of music-making as well as the perception of music as an informal activity for people to connect with one another.
The genre of jazz was founded by musicians without recognition and degrees but is mostly represented today by people who studied in these schools. It would be strange to imagine other genres like pop, country, hip-hop, electronic, rock represented by 'graduates' of their respective institutions, and what would that mean for range of creative output available to experience?