Possibly because they see the word "supercomputer." Possibly because they see all the listings on ePay asking for $3k to $30k for a single rack of an Altix system, and don't check the completed auctions... And just maybe because there's a lot of metal and commodity RAM in there.
Scrappers aren't stupid like technology writers for computer-enthusiast webzines ... they have to feed themselves selling what they buy. And I don't think they make their decisions based on phony eBay auctions, either
What's there to get ? Racks, numalink cables, maybe Itanic chips (are those soldered to the modules ?), and yup, you hit it -- commodity memory.
The thing is probably worth $1500 to a scrapper. It would be a stoopid waste of resources to dump it like that.
But then, that's what we can expect from our anti-intellectual elected officials these days, yes ? A supercomputer ? Symbol of extravagance. We could use the money to build some more prisons.