I remember reading an article some years ago that addressed this. Seems at one time there was no limit and a very large fusebox at a hotel caught fire. This was in the days of rubber covered wire & this produced quite a bit of smoke which resulted in some deaths. In order to limit the available fuel, it was decided to limit the number of circuits.
You should also see 90.8(B)
Few things are harder to put up with than the annoyance of a good example.