The short answer to that is that it's like the exhibition right: 1988 is a cut-off date and artists generally don't benefit from being paid for the exhibition of their works prior to then, except for a few organizations that do it voluntarily. And so it is with the resale right: unless there's a law that requires this, then artists will not benefit. The fact of the matter is that organizations that are out there engaged in reselling works of art are not interested in paying this, and so they need to be compelled to do that. Remember, it's 5%. It's actually a very nominal amount. If you look at the total cost of some of these exchanges, it's very minimal, and yet it has a huge impact on the life of an artist, particularly a financial impact.
On October 15th, 2018. See this statement in context.