There is some info about them on here:
https://www.archiveteam.org/index.ph...=Yahoo!_Groups
I think the reason they are doing this is because the Yahoo Groups' content was being removed and so the data on there would no longer be available. According to Wikipedia, all content posted to Yahoo Groups was due to be deleted on 31 Jan 2020.
https://en.wikipedia.org/wiki/Yahoo!_Groups
I would log into one of the groups that I belong to, to see whether all the content has actually been deleted, but I can never remember my username or password!