It had everything to do with what was necessary on set for the day. It isn't that he wouldn't hire a number of technicians to help him complete a film, but he wouldn't keep them hanging around when their job was done for the time being. It's a joke, but in one Kubrick biography, when he was making The Shining and the lighting guy was done doing what he had to do on the set, Kubrick sent him off to work on the lighting of his house.
It's also do to how long he would make a film. On Eyes Wide Shut, the billiard room scene with Sydney Pollack and Tom Cruise alone took weeks to film. Since Kubrick could pace himself, he could get certain technical things out of the way and just concentrate on how film the scenes. There he would have some camera people and a few other people on site all the time, but if the person wasn't essential for the day, they were not on set.
So, even though he was clever with number of people on set, it isn't like his cleverness is that useful. Typical films are shooting for more coverage in a given day and so lots of things have to be done tech wise to keep things afloat. Kubrick was able to get away with murder.