"Pardon him, Theodotus: he is a barbarian, and thinks that the customs of his tribe and island are the laws of nature." - George Bernard Shaw, "Ceasar and Cleopatra"
I regard that as a caution that just because I think something is reasonable, it doesn't mean that others will think the same. My sense of reasonableness is based on many things, including being part of a culture where it's cheap to record, store, and redistribute sound, and which regards anything old as being part of the public domain and therefore unrestricted.
Modern informed consent has a much higher standard than the consent of 100 years ago. For one, it's not just consent about the process of making a recording but informed consent about the larger consequences of doing so.
The people who were recorded likely knew their speech was being recorded for future scientific research. However, consider the technology of the time. The recording was onto wax cylinder, so it could only be played a few hundred times before being worn out. This limited the total number of people who could use it, and mostly to anthropologists. It was also hard to duplicate a wax cylinder recording with any fidelity.
There is no way that the people of 100 years ago could give informed consent of the possibility that their recording would be open to the world a century later.
While you, if you published a book, would have grown up as part of a culture which has had centuries of book publishing experience, and would be able to provide informed consent.
Of course, those people are dead, so why does it care?
Anthropologists also want to get a more complete view of people's lives. To do that, they may need to make assurances about how any notes or recordings will be used. If the standard is "after 100 years everything will be public" then anthropologists are less likely to get the information they want.