It seems as if an inordinate number of high and low pressure systems hang over Lake Superior. Why is this true?
It is true, but with this important caveat: Low pressure centers tend to stall in the vicinity of Lake Superior during the winter and high pressure systems do so in the summer. It has to do with the temperature structure of the lower atmosphere.
In the winter, the water of Lake Superior (or, more correctly, the Lake Superior, Lake Michigan, Lake Huron area) and the air mass over it are usually warmer than the air masses that cover the surrounding land area. Warm air usually brings lower air pressure than cool air. The opposite situation ordinarily prevails during the summer. Spring and fall weather situations can be either at various times.