There are so many conveniences around a global team name. Any time we played through the mental exercise of ambiguous names, it led us back to the deep pains of reading out loud security codes or fingerprints, or relying on some kind of hard-to-use web of trust around trusting people and then their vouching for teams. (note people, too, have unique names.)
With our testers, I've already had so many conversations about team names. If it's an in-person conversation it's validated entirely without looking anything up. If it's digital over an alternative medium - then the sharer doesn't have to go look up their team's identifier in order to talk about it. Everything is easier.
Also, I'm not that cynical by nature, but I've had a lot of conversations with people about security since we started Keybase. People don't check codes. From encrypted chats to SSH server fingerprints (ugg!) -- people don't check them. If a team name can be equivalent to one, but the cost is that the space is limited, it's worth it.
I guess in summary: why is a name better than a fingerprint? It can be memorized without effort. It can be visually or verbally reviewed without effort. And it often has meaning.