can anyone offer an explanation?
This site is the driving sales tool for new Zendrums. Selling new Zendrums is the primary source of income for Zendrum. It becomes problematic to compete with the aftermarket.
It was decided some time ago that it is not to become a trading ground for used instruments. If that happens, Zendrum the company spends money and resources maintaining a site which generates no profit. If you go to Zendrum.com, you already know of the Zendrum. There is no increase in worldwide visibility.
If sold via eBay or other channels, then the additional eyes who may not even be aware of Zendrum may become aware of the instrument and the Zednrum company does not have to get involved in sales disputes or clashes between buyers and sellers.
Zendrum makes and sells new instruments. Too many problems arise with third parties believing we endorse and police all aftermarket sales.
In short, when people sell Zendrums to each other on this forum, we get pulled in if there are any disputes, we don't get to sell any new instruments and no one new sees the instrument.