I've been regularly checking eBay/craigslist for good SO deals for several years now, and this kind of listing shows up now and then. I think the sellers just want to get a big check without having to do the work of breaking the collection and listing tools separately (or at least in smaller sets). The problem, of course, is that there's no secondary market for a $50K pile of tools.
There's a guy in Hanson, MA that has been trying to sell his SO rollaways with tools for $25K on craigslist -- and he's been trying for many months (or maybe years at this point.) He doesn't seem to have dropped the price at all. Baffling.
--Colin