Simply because of the administration and tracking of such things and also because we believe it would be more onerous to try and track it, private sales are not tracked, but public sales are easily tracked. The galleries, dealers, and auction houses are the only people who really sell publicly. They just have to remit 5% of the sales, which is shared between the buyer and the owner, to the Copyright Collective, which already exists in Canada. The Copyright Collective is responsible for remitting that payment to the artist and the artists are responsible for registering themselves with the Copyright Collective. It's actually an incredibly easy system to track and to administer.
On October 27th, 2016. See this statement in context.