>>6753216A few reasons.
For licensed sets like Jurassic Park, etc., it's probable that the set designers haven't seen the movie, or even seen finalized models from the movie. This is why so many capeshit and Star Wars sets don't look anything like the scene or vehicle they're supposed to be - the toy designers were only provided with rough initial sketches, which could have changed significantly by the time the movie is actually finished and released.
A second reason for the secrecy in licensed sets is because the licenseholders want to keep some of the twists a surprise. Imagine if in 1980, the Empire Strikes Back toys were released with a set called "Luke discovers Darth Vader is his father Playset" a month before the movie premiered.
A third reason, and I suspect this is the case for this line, is that the package designs haven't been finalized yet. Usually the first official leaked pictures of Lego sets use placeholder minifigs because the minifigs for that set haven't been finalized yet. This is why the leaked image of the Mos Eisley Cantina had a bunch of Squidward minifigs standing in for the Bith jizz-wailers. Considering that we're still two CMF waves away from the Unikitty wave (Lego Batman Movie wave 2 was just released, the summer CMF wave just leaked), it's possible that they haven't finalized the packaging.
