Because "haisha" means "dentist." It's a game about dentistry. From what we can tell, it's a Trauma Center type of game, except the traumas are located entirely within mouths, and seem more troublesome than traumatic. Not that we wanted to do any emergency oral surgery anyway.
Vol. 35 should prove to have wider appeal than the others: it's a DS remake of the PS2 Simple game THE Genshijin (Primitive Men), which is one of the rare Simple games to be released in the U.S. (as The Adventures of Darwin). It's a strategy-sim-type game in which you control a tribe of cavemen. The DS version happens to be extremely cute.