I see no reason why J.J. Abrams should not capitalize off of the success of the movie Cloverfield. If he wants to release a movie eight years later that is a close relative of the original, I say why not. Sequels are created all the time and this is really not much different.
Why do academics hang up their degrees? Why do athletes put their trophies on display? To toot their own horns. They are proud of their accomplishments and want people to know about it. The same is true for J.J. Abrams. He uses Cloverfield as a marketing approach for his movies because it was a successful movie and it helps remind fans and movie goers of the quality of work he produces.
J.J. Abrams has made a well-deserved name for himself by tackling science-fiction behemoths and cult classics such as Lost, Star Trek and, obviously Star Wars. Although Cloverfield holds a 7.1 rating on IMDB, it's not anywhere near the level of Abrams' other works. The story of a plucky group of near-strangers attempting to escape the wrath of a monster attack in New York (and why is it always New York?) may have some played-out charm, but Abrams' resume has many more interesting projects to draw on.
J.J. Abrams is a wonderful director who has a lot of successes in his past: the most recent being the extremely successful Star Wars movie. Why should he spend time using past movies that weren't very successful to market the even better movies? Yes, Cloverfield has some die hard fans, but most people weren't very into the movie.