May 26 is Memorial Day. It is the weekend all six of the originals were released, plus it was the initial target date for Episode 7.
The studios get less money from tickets with each successive weekend, so they try to maximize the first weekend's box office. By doing it on a holiday, they get to extend the number of people that can see it that first weekend.
Plus...by having it Memorial Day, kids can see it repeatedly once school gets out,
Plus...it gives plenty of time to market Christmas presents.
Plus...no...that's it.
