With the pre 2016 Followers gadget, the Followers population for a blog was managed through an Options link on the Followers gadget . This required the blog owner to sign into the Followers gadget, to access the Options link. Authentication - and an owner specific Options menu - is no longer a pert of the Followers gadget. It is possible to Block Followers, from a blog - the option is just not part of the Followers gadget, any more.
What Blogger won't tell you