The retail sales for the Universal Monsters set is under $25,000 (according to Blu-ray Disc Statistics), and the set has been out a few years. Dracula single release, on the other hand, has sales over $100,000. I hope they at least release some of the sequels as stand-alones.
I was just posting here a couple days ago about the sequels and their issues, and that Universal probably didn't see much of a return on all the work. You could've knocked me over with a feather when I read the latest!