I would assume it's purely financial, that anticipated sales wouldn't justify the cost. But, given how much they retail for second hand maybe I'm wrong and there's another reason.
yes I’ve been looking on eBay for around two years for these, there was a set of four that went for £400 in Germany last month and I forget to bid!. I was pig sick for a week afterwards!. There is a set of 5 for a ridiculous amount of well over £1500 on eBay USA. They just don’t seem to drop in price. I’m guessing the first one (possibly the most sort after) won’t go down in price and it usually sells for over £225. I’d like them but not that much. There are probably many 1,000s of new fans since 2007 and I’d bet a lot of these are wanting these as much as I do!.