The reality is that the economics don't work. Many of these boats have leaks that have caused the deck cores to rot. It's actually cheaper in most cases to make a new deck molding than to rip it apart, recore, and refinish. Raw materials are more for brand new, but labor is considerably more for recore. I don't know about the upper end, but at the trailerable end, if a recore/refinish is needed, the price to do it professionally brings the price of the recored boat up to the price of a new. As a customer, which would you choose?
Stuart buys sound hulls, and only half the deck is cored in a Mariner. Say Stuart buys a Mariner hull for $1K. It doesn't need recoring, but just the refurbishing (standing & running rigging, decent sails, cushions plus polishing, cleaning, and painting) is going to push the selling price above $12-15K, depending on what the buyer wants in the way of refurbishing. With the average condition used Mariner going for $3K (nice condition might get $5K), there are only a limited number of buyers willing to pay that much of a premium for refurbishing. And there are even fewer buyers for a new Mariner - $50K for a "sail away" package.
On the other hand, Rhodes 19s (use the same hull as Mariner, but keel instead of CB, cuddy instead of cabin, more complex rig) are actively raced. Therefore there are new Rhodes 19s sold every year, which keeps Stuart open. Another example: Flying Scots also sell new hulls every year because of demand from racers.
Fred W