I wouldn't be surprised if they aren't selling too well.
Once a handful of people pick them up, they get uploaded elsewhere (torrents, russian fansites.., dropbox's between friends) and everyone downloads them.
Unlike the early DSP shows where people were like "Shit, I've gotta rush to merch and grab a DSP CD before they sell out" - now its just "Meh, I'll download it online somewhere later"
From a business point of view, there is probably someone crunching the numbers and they've found its not worth the cost of paying Pooch and Dylan to mix DSP's, then the server costs, not to mention venues often fight for a cut of the profits too.
If and I mean IF WB does bring back DSP's, everyone needs to make sure that if you want a DSP, you actually buy it and not torrent it. WB don't care about fan interest, they just care about sales. Thats the only way we'll keep this alive.
(None of this is directed at you Mark, or anyone else lol, just talking in generalities. I know there are hardcore fans that buy all the DSP's)
EDIT: I figure I'll get in and say this before other people try to correct me. I know on various occasions the band have said they support the sharing of live material. I even remember a few threads where the band were ok with DSP sharing. But if I recall correctly, management tried to remove all evidence of those threads. Which shows that, whilst the band is ok with it, management aren't. They can't make any money if people are just sharing the shows, rather than buying them. And at the end of the day, although LP makes the music, WB owns it...
Bloody hell, I could be a WB rep.