Ammo makers are not big enough to keep all ammo in production at all times. They set up a line for a caliber, run off a batch big enough to last through the cycle, then tear down that line and set it up for another caliber, and so on. If all goes as planned, they will get back to the first caliber just as the stock room and distributors begin to run out of it.
But if a given caliber is selling so fast they can't keep up, they will keep that line running, even changing other lines over as needed, and defer less popular calibers to another day (or year). When they can get a break, they will run off the next most popular calibers, and so on. When will they get around to some of the less used calibers? Who knows? Maybe they will just use the situation to discontinue rounds like the .32 S&W, the same way they used WWII to discontinue poor selling and low profit calibers.
Jim