How has every franchise dropped? They're still going strong with X-Men spinoffs, Captain America & Thor sequels, an Ant Man movie, etc. We're going to be seeing a lot of Marvel for a very long time. Why? Well for one thing, there are contracts to complete several more movies but even more importantly because they're making money...they're popular and aren't fading at all.
DC on the other hand has been pretty weak in the movie department. The general public sees movies, not animated TV specials, so that's what a theme park would want to bank on. The Green Lantern was awful. The Superman reboot underperformed critically and commercially. There have been no green lights for Flash or Wonder Woman films yet because of the failure of these last two films.
While The Dark Knight trilogy was a huge hit, it wasn't because of the property but because of the director--Chris Nolan brought something really special to the screen and no matter what characters he was working with, he was going to have a hit (notice the first film is the lowest grossing of the three--the interest for Batman wasn't high until word of mouth spread about the films themselves). You can tell DC knows this and lacks faith in their brand by marketing the heck out of Chris Nolan's position as executive producer for the upcoming 'Man of Steel' (Superman reboot 2.0)
Though it may not have been a proactive decision, Universal made the right choice, and I can assure you Marvel will be around for quite a while longer.