The whole point is that you don't just use it to upload a key. You link various verified identifies of yours across the web to your Keybase account so people know the PGP key there is the one of the verified person. It's a way to tie all your verified identifies together.
If someone would manage to compromise a bunch of identities of someone on the internet, and then create a Keybase account with them and then upload a compromised PGP key that would be a problem if you don't verify the key. But that's a bit of a stretch.
My real wish is that keybase supported ssh keys and would provide them as an agent.
I do agree on the ssh key feature being nice, and, here's a link: https://keybase.io/blog/keybase-ssh-ca You could also just use the keybase file system to keep ssh keys around.
Not to mention it's notoriously slow and has been shown to be an insecure method of distributing keys (due to the fact that anybody can upload any key).