That may not be a thing of any sort. JFK was shot in 63. There's a 'fifty year rule' for documents, but it's kind of a minimum rule, since the archivist can extend the time period longer at what appears to be their discretion. Since 50 years would have been up in 2013, it would seem that this is a bit late, but there are plenty of viable reasons why that might be the case, including, "so what?"

Basically, most of the documents are probably released already, some would be related to LBJ, and therefore could have been sealed longer, while others might be sealed longer for other reasons. Still more might be due to the archivist not getting around to what amounts to fifty year old documents of little interest.

The reason to release them is clear, as DrBobby stated.