My very naïve understanding is that in the keybase model there's no master, just several keys which can sign each other, so you can lose any of the keys (as long as it's not all of them), unlike in the PGP model, where you can't lose the master.
In practice, though, as long as you protect the master key appropriately, the PGP model isn't that much worse (and possibly in some ways better — I'm not sure what happens in the keybase model when one of your devices is compromised, rather than just lost, and you don't notice for a while).
In practice, though, as long as you protect the master key appropriately, the PGP model isn't that much worse (and possibly in some ways better — I'm not sure what happens in the keybase model when one of your devices is compromised, rather than just lost, and you don't notice for a while).