The copyright last 70 years after the death of the author, so 170 years would be rare (indeed 190 years would be possible). This was an implementation of a 1993 EU directive:

https://en.wikipedia.org/wiki/Copyright_Duration_Directive

That itself was based on the 1886 Berne Convention. "The original goal of the Berne Convention was to protect works for two generations after the death of the author". 50 years, originally. But why? Apparently Victor Hugo (he of Les Miserables) is to blame. But why was he bothered?

Edit: it seems the extension beyond the death of the author was not what Hugo wanted. "any work of art has two authors: the people who confusingly feel something, a creator who translates these feelings, and the people again who consecrate his vision of that feeling. When one of the authors dies, the rights should totally be granted back to the other, the people." So I'm still trying to figure out who came up with it, and why.

So far as I can tell, the idea behind extending copyright two generations after the author's death was so that they could leave the rights to their children and grandchildren, and this would keep old or terminally ill authors motivated.