Let's say you want to rotate keys, because you suspect it's been compromized. I'm a user who follows you so I would like to know the new key
Who's social graph does my client use to know the new key? If it's yours, then that graph could have been altered after the key got compromized, so it's not reliable. If I have to rely on my WoT, then somehow the people that I follow/trust would have to overlap with the people that you follow/trust