Oh, perhaps you hadn't heard? The reason I'll probably never delete the comics blog is because of this. That entry is quite possibly the most linked thing I've ever done on the Internet. Ultimately, the reason is because I had the foresight to quote Bob Greenberger from a thread on the Collected Editions Discussion Forums. It was where he explained the reasons for excluding certain material from the Showcase Presents line at its inception.
DC pays a royalty based on a percentage of the cover price to writers, pencillers,and inkers to all material published prior to 1976 and after 1997. For the period in between, the vouchers that were in use called for a set reprint fee to be paid. In some cases, the amount of contractually obligated reprint fees makes the budget for a proposed collection unprofitable. In those cases, DC will either scrap the project or ask the talent involved to waive the reprint fee in lieu of the standard royalty arrangement. If the parties agree, then everyone benefits.
So how do things stand now? Well, DC has reprinted comics from after the stated "1955-1975" window in that format, but this has either involved a) re-negotiating reprint fees with the talent or b) material from deceased creators. There seems to have been a bit of a snafu involving those reprint fees after Bob's forced departure from DC editorial, which led to several books being solicited and then cancelled prior to publication. As of this writing, none of those affected books has seen the light of day.
I tend to run hot and cold on Showcase Presents. I sometimes miss the color, and it can be intimidating to try to wade through the sheer volume of an average one. But I'm glad to know those books are out there, because the majority of them have been devoted to some of my favorite comics of all time.
I just wish I had given that blog entry a better title.