Do you have a reputable source for this from the Internet Archive (not speculation)?
It literally says that the Internet Archive deleted their account, not Flickr.
Unless the support thread is wrong, I don’t see how your claim about no consultation and no warning is consistent.
https://www.flickr.com/help/forum/en-us/72157720510495566/#r...
"The Internet Archive Book Images recently deleted their Flickr account. >Flickr and Internet Archive were in agreement on this< because:"
https://www.flickr.com/help/forum/en-us/72157720510495566/#r...
"Hey, all. We're sorry for what seems like a sudden removal of the Internet Archive account. This decision came after weeks of conversation and coordination with the Internet Archive."
For many with lighter copyright you can certainly host them elsewhere as well.
1. All the lost metadata. By making the images available on Flickr users were unearthing the interesting images from the 5 million plus collection and creating all sorts of valuable metadata.
2. There is no way to explore the images as they are stored on IA. At a certain point if the data can't be explored it may as well not be available.