How do you propose to supply the home school teacher with the appropriate book to check the work of the homeschool student? That is the purpose of the teacher's edition. eBay is making it impossible for the homeschool teacher to purchase the required editions.
E-bay is not the only source of these. Buy them direct from the publisher or another retail outlet that supplies teachers.
I guess I don't really have a problem with this. There are some unscrupulous public school kids who like to pick up teacher's editions. Perhaps this will make it a bit more difficult for them.