This may be the case at other lines, but not the four mentioned.

In the case of Göteborg–Kiel there is only Stena Line, Helsingør–Helsingborg are two companies and three osm lines, for  Świnoujście–Ystad the operator-tag of both lines is "Polferries AB / Unity Line Sverige" and for Frederikshavn–Læsø the operator of both lines is "Færgeselskabet Læsø K/S"