It is not possible to install a spiral staircase in all buildings. Different building law requirements in the various federal states often mean that straight staircases are prescribed and installed as rescue stairs / fire stairs.
Other possible arguments in favour of straight staircases are the necessity of enabling large numbers of people to escape and using the given advantages of staircase geometry.
It is, however, also often architectural reasons that are decisive when manufacturing a staircase tower with two or four supports. If gratings are used to brace the central supports, they give the impression of a stabilising wall and give the staircase its own character.