Why can't the Dan Dare Corporation just keep Dan Dare and sell everything else? It's not as if they're doing anything with Doomlord and Bloodfang.
I'm just guessing, but Dan Dare stories often started on the covers of Eagle and continued inside, so to fully own all the Dan Dare story pages, DDC would have had to buy the rights to the Eagle logo and any characters that appeared on montage covers alongside Dare, so they may not be doing anything with them, but they still need to retain ownership to do anything with the pages they share with Dan Dare. I gather from comments from those who've had direct dealings with them that DDC - a husband and wife team - are at best ambivalent towards the other Eagle characters, and don't want to dilute their business model.
It's a damn shame, as one of my all-time fave artists, Jose Ortiz, was pretty much a permanent fixture in the New Eagle for about 7 years on various strips, and we'll never see collections of that work - or Alan Hebden, Carlos Ezquerra and Mike Dorey's
Comrade Bronski, which admittedly wasn't the greatest strip ever, but if you don't want to own a graphic novel that answers the question "what would Dirty Harry be like if he looked like a member of the Human League, drove everywhere in a dune buggy, and fought the KGB in Cold War-era Moscow?", then buddy, you and I are very different people.