Shouldn’t all these authors be investigated by the police and possibly prosecuted and/or sued?
I'm not a lawyer, but I can tell you what the penal code (PDF) says:
Section 8 - Invasion of personal reputation (531/2000)
A person who unlawfully
1) through the use of the mass media, or
2) in another manner publicly
spreads information, an insinuation or an image of the private life of another person, so that the act is conducive to causing that person damage or suffering, or subjecting that person to contempt, shall be sentenced for an invasion of personal reputation to a fine or to imprisonment for at most two years.
The spreading of information, an insinuation or an image of the private life of a person in politics, business, public office or public position, or in a comparable position, does not constitute an invasion of personal reputation, if it may affect the evaluation of that person’s activities in the position in question and if it is necessary for purposes of dealing with a matter with importance to society
As I understand it, there needs to be an injured party; the police won't initiate an inquiry on their own. Thus the private lives of dead people, for example, are fair game.
If everyone made full use of this law, I'd imagine that at least some biographies you can find in your local library would give cause for a court case. I think the law goes too far in protecting people's feelings at the expense of free speech, so I'm happy that in practice it doesn't work out that way.