According to Google Maps, Abrams's production company Bad Robot is located on the corner of
W. Olympic and Camden Avenue and is about 3 miles from
Cloverfield Blvd in Santa Monica.
It may just be a street name they see all the time and liked. Also,
Santa Monica airport used to be named Clover Field.
Don't know if it is accurate but
this page claims to have an email saying
that "Cloverfield" was just a code name and that they planned to eventually announce a different title but then it leaked out and all the movie geeks knew it by that name so they decided to leave it that way.