This is complete speculation, but I think the Body Blast series probably made Cathe and SNM second guess using premixes on the Hardcores at all. Remember how it seemed like a long time for the Body Blast series to ship and many questioned the cause of the 'hold-up'? I remember Cathe or Chris posting about having to preview each and every premix to make sure they were 'okay.' And we all know how many premixes the Body Blast series contained, so I'm sure this was no small undertaking. So the series finally did ship, and people complained about the premixes and having to wait for the next chapter because of the 'insert cards'; people complained about the lack of certain premixes, and some complained that there were too many premixes. Because these DVDs contained so much 'stuff' there was often a small 'pause' as the disc switched to the next layer (someone who understands DVDs and their make up could better clarify, I'm certain!) (like the pause that comes in between step sections 1 and 2 of SJ&P) - so some folks sent their discs back. Then, the Hardcores, again, seemed to some to be taking too long to ship, so people complained. I have a feeling that after some of the 'issues' the Body Blast series created (like the Workout Blender not working for several folks), Cathe wanted the Hardcore DVDs to be single layered and probably thought of eschewing premixes all together, to ensure single layeredness (is that a word?).
Also, remember how Cathe said she had two editing teams working on the Hardcore series? I think Cathe felt so much pressure to get these shipped quickly, that 'perhaps' corners were cut. I'm not saying anyone is in the wrong for complaining or for having expectations, nor am I saying I'm not happy with the Hardcores, because I absolutely am happy with them - I'm merely saying that it's probably extremely frustrating for Cathe (and SNM) to keep folks happy. I think Cathe truly wanted to ship the DVDs as quickly as possible last time around, which is why, to some, the premixes and chaptering were less than they've come to expect from a company of SNM's caliber.
Good gravy, does this verbose thing have a point? Just that it's hard to please everyone and I think it's sad that Cathe feels pressure to rush stuff in order to 'appease the masses.' Again, my sentiments are mere speculation; this is just one Cathe fan's opinion.