The reason MVC unenrolled weeks, resale or bought direct, are treated differently from resale Sheraton and Westin is that the take-up rate of MVC weeks owners for enrolment was terrible, really, really terrible. It was a difficult "sell" to say to people that they should pay even a few thousand to enrol, or buy club points to enrol when you look at what your week will elect for and find it won't get you what you can currently get when booking your week. There's a lot more depth to the value proposition for enrolling and electing for club points, but the conversation quickly gets derailed by the basic "I can't get what I've got" problem unless the salesperson is better than any I encountered. Even after enrolment was available for no up-front cost, many owners were already in the "Its not worth it" camp. Each MVC ownership needed a contract revision to be enrolled, so each owner needs picking off to get them to move over. The "free" enrolment option was not offered to European owners, like it was for US owners, and fees or requirement to purchase points was required until recently. The website no longer states this and I haven't asked whether it can now be done without a fee or additional purchase now.
With the deployment of the MVC Destinations Club (aka Abound) to Sheraton and Westin owners they needed to find a way to avoid the terribly slow uptake rate that picking off owners one by one requires. So they went with an agreement between VSN and Abound, which then drew in all owners who had access to VSN as at Aug 2022, which included resale mandatory Sheraton and Westin owners.
