As a guess, they may need to give ticket vendors a chance to get their systems up-to-date so that tickets for all games can be made immediately available once the schedule is publicly released. I don't think they want a situation where an NBA fan says "Look, the NBA officially has a game on my birthday on Nov. 23rd with my hometown team coming into town, but I can't buy tickets!!! What the heck is this crap?!?" But of course, once the ticket vendors get the schedule, stuff gets leaked.