That’s not what that rule says. It says you shouldn’t “encourage users to purchase content on another platform”. Ignoring the first part of that sentence is disingenuous. That rule is to prevent people from using this storefront as basically free-advertising and then saying “hey, go here for a better deal!”.
It doesn’t say you aren’t allowed to link to external access for the source files. Staff already said in this very thread you could. They obviously just don’t want a situation being created where the market-place is abused with people frequently encouraging people to head to a third party site.