Marvel/Disney announce them, promote the heck out of them, and then release them soon after. They also promote the characters through cameo appearances, which leads to solo films, which then leads to team-ups and team films. Plus they keep the public excited about their product, by putting out several blockbuster Marvel films every year, strategically spread throughout the year, so that one is opening as another is fading out.
DC/WB announce possible films that won't even be cast for several years, and often don't ever happen, featuring characters the non-comic-reading general public isn't familiar with, without introducing the characters first, and featuring actors/actresses most people aren't yet familiar with, or who most people hate. Sure, DC has the big one-two punch. Batman and Superman will always be big draws. But other DC characters? Not without the type of visual promotion rival Marvel employs.
What do you get more excited about, possible films with sketchy release dates far in the future, featuring obscure characters and unannounced actors/actresses, or action-packed previews of soon to be released films, featuring the actual cast and a set release date?
Of course, the one problem both companies share is their habit of casting Ryan Reynolds. Stop doing that!
©2014 Denim McDemus