I think the short notice certainly has an impact. There was a lot of build up to the pre-sale of Carnival with artist previews and a lot of chatter. I knew this one was coming, but it still seemed to come out of nowhere. Knowing you have a good shot at a case in August is also probably slowing things down a bit.
The slow eBay sales for Carnvial sketches may also be slowing some people down a bit. I'm sure that is not stopping the usual dealers, but it might be stopping some people that thought Carnival was going to be a 'double your money in one weekend' rip and flip.
Personally, I'm very intrigued by the idea of INSECTEA and THE DEEP but I think 1000 is just too big for niche sketch releases like these and will probably sit both of them out. There will be singles galore available when they release so I can always pick and choose a small collection if I'm so inclined.