Jaime is the most well-known Blue Beetle given he's the only one that's had significant exposure in media outside of comics. So, its an easy pick for a movie.
IMO, this movie is long overdue. The first Jaime Reyes series was pretty good and the character has a very interesting mythology (which was brilliantly tied to the original Blue Bettle- Dan Garrett). Not to mention that Jaime has kick-ass look and I really wonder why it even took this long for a movie.