Existing guidelines mention:

1)  All kiting should be confined to the southwest corner of the LZ.
2) If pilots in the air are observed to be setting up their downwind, base, or final approach, all gliders should be grounded. This helps to indicate to pilots in the air that those on the ground can see them making their approach.

People not respecting existing guidelines is the main issue. Also, independent pilots (not just students) may be kiting without instructors present, so it is not just a school/instructor issue.

Extra info: This is the USHPA web page referenced. It states (but not where the accidents happened)…

One case involved a midair, and the other involved a collision between a kiting glider and a glider coming in to land..